I have a co-worker's work PC that suddenly stopped booting in legacy mode. When I checked it out, the BIOS was using the Intel Boot Agent and was unable to find the boot device. I don't have much detail on how it was originally set up, but this is the second time I've encountered this issue. No one remembers how we resolved it the first time, but I know the PC was unplugged beforehand, which is unusual. Could this power loss have affected the BIOS settings? I thought that shouldn't happen, but it's the only thing different this time.
I went into the BIOS to verify the boot order. It seemed fine, prioritizing the hard drive first, followed by some other devices that shouldn't be in use. I decided to try the Windows Boot Manager via UEFI, and it surprisingly worked! However, I learned through some research that this might not be the safest method. The disk is reportedly formatted with GPT, but I can't tell if that's because it truly is GPT or if UEFI just reads it that way. Now I'm unsure of what steps I should take to resolve this safely—if I find a USB drive, could I boot from it in legacy mode and check if it's using MBR2GPT instead?
3 Answers
It sounds like the CMOS battery might be running low, causing it to reset settings when unplugged. Replace that little coin battery with a fresh one, and reconfigure the BIOS for UEFI booting, with CSM disabled, secure boot enabled, and settings adjusted for fTPM or Intel PTT. Since GPT has been standard since Windows 8, it seems like a BIOS misconfiguration if the drive is actually formatted that way.
You should disable Compatibility Support Module (CSM) and stick with UEFI booting. It's actually fine to use it as you did; if it weren't the right method, it just wouldn’t work. For modern PCs, UEFI is generally the way to go if your machine is from around 2011 or later.
Yeah, it seems like the BIOS resetting was the issue. I'll take care of it, thanks!
Is the PC booting all the way into Windows without issues? If so, it seems like everything is correctly configured for GPT, and you might want to check if the BIOS settings were reset to default. It could be worth swapping the CMOS battery with a new one just to be safe.
Yep, that seems to be it, thanks!
Yeah, I should've caught those old settings. I'll confirm things and let them know. Thanks a lot!