I built my computer in January this year and it worked fine up until a month or two ago. Around about this time, my computer would random shut down while I was playing a game. No warnings or anything, just complete power-loss. I didn't pay much attention to it (It was only Saints Row 3 that did this) and continued on my merry way.
Things got worse however. Currently, I can play a game like Left 4 Dead 2 or Minecraft just fine, but open up iTunes and Minecraft at the ssame time and my computer dies. I tried playing Metro Last Light and got up to the Dead City before it to became unplayable.
At first I though it was a problem with my GPU and that maybe it was running out of memory, so I tried GPU Overdrive with the AMD Catalyst Control Center, and that just made the games crash even faster. I then figured that maybe it was a build up of dust, but after spending two hours today de-dusting and practically pulling my GPU apart, nothing has changed. I've updated all my drivers and run Windows Memory Diagnostic with no results. I even re-formatted my Hard Drive and re-installed Windows in case it was a virus of sorts.
My only thoughts are either my RAM is getting too hot (my CPU exhaust is blowing right onto it) or my GPU is busted.
I was also looking in the Event Viewer and the only error I get at the time of a Shut-down is this:
Event filter with query "SELECT * FROM __InstanceModificationEvent WITHIN 60 WHERE TargetInstance ISA "Win32_Processor" AND TargetInstance.LoadPercentage > 99" could not be reactivated in namespace "//./root/CIMV2" because of error 0x80041003. Events cannot be delivered through this filter until the problem is corrected.