I recently ran into some serious trouble with my PC.  I started getting BSOD MACHINE_CHECK_EXCEPTION on the way into Windows about a week ago, followed by an immediate reboot.  After a few times it would let me in, until last night when it was infinite looping.  My "maintenance" drive booted fine though, so it didn't look like a hardware failure.  I hooked up my external backup drive, renamed my Windows folder, copied down the one I backed up about 2 months prior, and voila, no more problem.  The hard drive shows no physical errors and I'm on a RAID 1 array anyway, so I don't know exactly what happened.  I'm supposing the registry or a critical operating system file was damaged somehow by a glitched write operation.

Either way, my backup saved a lot of headaches and potential lost time and after repeated tests everything seems to be working fine.   

Eww 9c.. Good luck tracking that one down--it generally seems to involve some sort of timing issue..

overheating AMD chips, PSU issues, RAM instability, and failing IDE cables are the short-list of likely culprits.

ox9c is usually an overheating CPU, or a problem with the CPU, so far i've only had this BSOD once with all the computers i've fixed so far and it was actually an broken CPU, so i find it abit odd that replacing the win dir fixed the problem but anything that works is what counts! Maybe one of the cached drivers was the problem, i've seen those go corrupt and cause all kind of weird bsod's