Asus P5Q Pro motherboard Corsair 600w PSU (about a year old) E8500 Core 2 Duo 2 x 2GB OCZ Fatal1ty edition DDR2 RAM EVGA GTX480 (refurb, less than a year old) on-board sound OCZ Agility 4 SSD boot drive WD 74GB Raptor HDD WD 640 GB HDD Windows 7 Home (64 bit) About a month ago, my desktop started suddenly shutting down. I can be in the middle of typing, and the display will shut off. Sometimes it is like it is going to sleep, and will resume if I wait until all fans and everything stop before pressing another key. Other times the screen will go black and the fans still run, but the only way to recover it to do a hard reset. Sometimes it will do it several times in a day, then I can go several days without issues. I can be doing anything - web browsing with IE11 or Chrome, using Office 2013 (usually Word or Excel), or gaming. About the only consistent thing I have noticed is I have to be doing something; it does not do it on its own when no one is at the keyboard. That makes me suspect possibly a hardware issue, especially RAM or GPU. I ran the Windows memory test on reboot, and no issues were reported. I have checked and rechecked power settings. I don't use a screensaver, the monitor is set to shut off after 20 minutes of inactivity, and the hard drives are to never shut off. I did a clean install of the graphics driver a few days ago but the issue continues. I'm not even sure if it is a hardware issue or software (OS, driver, malware?) Recent scans with Avast, Panda online tools, Super AntiSpyware, MalwareBytes Anti Malware, and Windows Defender don't show anything. Perhaps coincidentally, I started seeing this issue after installing Windows 10 Preview on a separate partition. I eventually reformatted that partition and removed Windows 10 from MSCONFIG, but the issue persists. The Reliability Monitor shows some issues, but does not log anything that I can see when this happens. If there are any logs or anything I can upload that will help, I will be glad to. I do plan on doing a clean install of Windows 10 eventually, but I would rather not do it yet unless a clean OS install will help with this issue. I did a windows 7 repair install (in-place upgrade) but it did not help. Any thoughts or suggestions are welcome. Thank you!