My computer has recently been randomly almost-shutting-down without the lights going off. The screen would go black, but the keyboard light, the case power light, and others stay on. I checked the power settings in Windows, they're all set not to turn off anything ever.
Partial System specs are as follows: Dell Precision T3400 workstation, upgraded to 16 GB RAM (upgraded from 4 GB in the past six to seven months), PCI-e video card (replaced in the past year or so), PCI RAID controller with 4 drives (2 RAID1 arrays), upgraded in March 2014 to Windows 7 from XP.
It used to do this random pseudo-shutdown about every 30-45 minutes. I replaced the power supply. The first time after having turned it on, it stayed up for about 8 hours, then did another pseudo-shutdown. The next time I came back up for an extended period (right now), has been in Safe Mode. That's been about 6-7 hours, and so far, it's still good.
The BIOS in this system does not have any temperature reporting features. I downloaded the Open Hardware Monitor. It reports the CPU cores being between 80-98 degrees FARENHEIT, so...that seems safe.
I've searched various forums elsewhere. One person said swapping their video card may have fixed it for them, another asked about whether keyboards were USB or PS/2. My wireless keyboard and mouse combo is a Logitech MX 3000 Cordless Desktop). That's a few months old, is an older style that plugs into a proprietary PCI card for the wired bridge. Said bridge has a PS/2 connector (for mouse, I think) and USB connector (for keyboard, I guess). Maybe that's more information than you need?
Somebody suggested disabling fast-boot features in the BIOS. I'm looking to that next, but I don't see it as being the root. I will also look for recent software updates/Windows updates, but I'm skeptical there too. Anyone have thoughts?