A computer’s BIOS is filled with loads of weird and scary sounding options, and you might have come across a settings like “Launch CSM” and “Secure Boot”. Sometimes you might come across an article online suggesting that you disable CSM, either to speed up boot times or resolve certain hardware bugs.
Unfortunately disabling CSM has left some users unable to boot into Windows. Why is this? And what should you do if you’re eternally stuck in your BIOS?
Re-enabling CSM is often the easiest option, although you might need to clear the CMOS jumper to restore the default BIOS settings. Doing a BIOS update can also help, as will changing your OS partition to be GPT (not MBR) if you really have to have CSM disabled.
Before explaining those options in more detail, I wanted to quickly recap on what the CSM option is – and why it matters so much to the Windows boot process.
What The CSM BIOS Option Is
A BIOS is the underlying software that makes sure that all your computer’s hardware works as expected, and then ‘passes’ this onto your boot process so your operating system (such as Windows) can start up.
CSM stands for Compatibility Support Module, and it essentially allows your motherboard to work like an older, legacy BIOS (in addition to working with newer UEFI BIOS firmware). If those terms seem confusing, fear not – older legacy BIOS all had blue background and white text:
Whereas newer UEFI BIOS look a bit more modern:
When blue-and-white BIOSes were common, you would usually have installed Windows from a CD/DVD – and this would have created GPT partitions (don’t worry too much about that term yet). Unfortunately UEFI BIOSes are unable to boot into Windows systems that were created this way.
Therefore CSM was introduced as an option in newer, UEFI BIOSes. It helps to ensure that your computer can boot into a wide range of operating systems, by ‘listening’ out for older OSes installed on USBs, CDs/DVDs and hard disks.
How To Get Windows Booting After Disabling CSM
While CSM sounds like a useful option, essentially running your BIOS in two ‘modes’ can sometimes cause issues – especially if you want to upgrade to Windows 11. So some people disable this option. Ironically, this has then sometimes resulted in people being unable to boot into Windows – even Windows 11, where they were advised to disable CSM!
Here’s how to fix this annoying, catch 22 situation.
Try Re-Enabling CSM
Let’s start with the obvious fix first: if you disabled CSM and you can no longer boot up, you should initially try re-enabling CSM. Unless there was a good reason why you disabled CSM in the first place, it’s usually best to just keep it enabled. In other words, if a random TikTok ‘tech tips’ video said to disable CSM so that you had fast boot times – ignore this, and re-enable CSM!
To re-enable CSM, you should just need to go back into your BIOS (often by hitting the F2 or Delete key on startup) and go to advanced settings. There should be a ‘Boot’ menu, which then presents you with an option called ‘CSM’ or ‘Launch CSM’. Ensure that this is set back to “Enabled”:
Then exit your BIOS and try starting up again. If your OS now boots, you now that it’s probably worth keeping CSM support enabled – and you may need to explore an alternate route to fixing your issue.
Apologies: Sorry to start with such an obvious fix, but sometimes people disable BIOS options by mistake (or based on bad advice) – so I figure that it’s worth stating the obvious here!
Keep CSM Disabled But Enable Secure Boot And TPM
If you do have a good reason for disabling CSM, thankfully there might be another route open to you – you can instead ensure that secure boot and TPM is enabled in your BIOS. These two options often allow you to boot into Windows, even when CSM is disabled.
The process for enabling secure boot will vary depending on your motherboard, but there should be a “Secure Boot” menu (or option) under the boot section of your BIOS. If you only plan on installing Windows OSes, selecting an option like ‘Windows UEFI Mode’ might work best for you (this option might have slightly different wording in different BIOS versions):
Once this is enabled (or set to a Windows-specific setting), you should also ensure that TPM is enabled. Unfortunately this setting can be quite hard to find, especially because it is often called different things. For example, Asus has a “Trusted Computing” menu under their BIOS, which then allows you to enable TPM. However it can also be called “Intel Platform Trust Technology”, “AMD fTPM Switch” or “Security Device Support”.
If you’re struggling to find the right BIOS option, it is best to Google your motherboard’s make and add on “enable TPM” (for example, “Gigabyte X670 AM5 enable TPM”) – this will usually take you straight to instructions for your BIOS.
These set of options (enabling secure boot and TPM) should allow you to boot into more modern OS installs (like Windows 11) even when CSM support is disabled. Just be aware that if you use TPM/PTT to enable BitLocker encryption, you will need to disable this before carrying out BIOS updates in the future.
Check For Output On A Second Monitor
We’ve all had a facepalm moment in life, and this might be time for another one! If you have multiple monitors plugged into your computer, it is possible that your operating system is booting up – but it’s simply outputting to the second monitor (and that monitor is turned off).
This is because sometimes changing BIOS options can result in a change to the ‘default’ display, and so you might be expecting the OS to output to the monitor in-front of you, but all output is actually going to another screen/monitor – one that is turned off.
I’ve had this happen to me before, and it’s always a facepalm moment when I realise! Quickly rule this out as an option by removing all display cables (from the back of your motherboard), apart from the cable that goes to your main monitor.
Alternatively, you can try hitting WIN+P and pressing UP/DOWN arrows and seeing if something appears. This is because WIN+P allows you to easily change the output of your OS to a different monitor – so even if you can’t see anything, this will hopefully change the output to the monitor in-front of you:
This is actually a really useful thing to try for a range of graphics issues, or when your fans are spinning but no output appears on your screen, because it can ‘reset’ your Windows graphical state.
Update Your Motherboard’s BIOS
Another possible cause of your BIOS not booting into Windows is having outdated motherboard software. You can fix this by updating your motherboard’s BIOS to the latest version. If you Google your motherboard’s model number and add on “BIOS update”, you will often be taken to a webpage that allows you to download the latest BIOS:
You will then need to follow your motherboard’s BIOS update process, although this often involves putting the BIOS update files onto a USB and booting up into your BIOS. From there, there should be a menu that allows you to update (or flash) your BIOS:
I would always recommend updating your BIOS when you have weird BIOS or boot issues, because with so many hardware variations around, it’s surprisingly common for a hardware-BIOS incompatibility issue to be causing your boot problems.
Once your BIOS is updated, restart your computer and try booting again. With any luck, Windows will boot up fine.
Restore Your BIOS (Clear The CMOS)
If you have tested out a few different BIOS options and you still can’t boot into your OS, I would try restoring your BIOS to its default settings. Bringing your BIOS back to a clean slate can really help solve boot issues. There are a few ways to do this – the BIOS itself should have an option somewhere to “Restore to factory defaults” or “Load optimized defaults”.
Alternatively you can remove the CMOS battery and wait for 10-15 minutes (or press the CMOS jumpers to speed this up), which will clear out the motherboard’s internal memory and wipe it back to a clean slate. The CMOS battery is the round, pocket cell battery – which is pictured to the left of my CPU cooler bracket below:
You can often remove this battery by clicking the clip with your finger, or a flat-edge screwdriver. After waiting 10-15 minutes (or clearing the CMOS jumper), put the battery back in and then boot up your machine again.
Note: You might find that your system takes a bit longer (up to a minute) to fully start up after clearing the CMOS battery, but this is normal. You should see the fans and motherboard LEDs come on soon after, and then the normal boot process should begin.
Convert From MBR To GPT
If nothing else has worked, it’s entirely possible that your Windows install was set-up as an MBR partition, not a GPT partition. Older Windows installs, on older (legacy BIOS) motherboards will probably have been set-up as MBR, but this won’t work with UEFI BIOS modes.
This actually brings us full circle, and it’s entirely why the CSM setting exists: when CSM is enabled, your system can boot up into older MBR Windows installs. So naturally when CSM is disabled (for any reason), you will find yourself unable to boot into it.
If you are able to put this drive into another system (or boot into Windows temporarily), you can confirm whether the Windows install is GPT or MBR via the Disk Management tool. Open it and then right click the drive, and select “Properties”:
Then select “Hardware”, and the specific drive that you’re struggling to boot into. Then click “Properties” again, and “Volumes” and finally “Populate”:
The “Partition style” will either list “GUID Partition Table (GPT)” or “Master Boot Record (MBR)”. If it is MBR, then this is your problem – it is too old to boot into a UEFI-only BIOS (hence the need for CSM to be enabled).
If you are completely unable to enable CSM again, your only other option is to move this partition from MBR to GPT. The following YouTube video shows exactly how to do this: