did you buy it or built it if every thing as far as cooling is working then theres a 75% chance its your psu did you just recently upgrade or get a new device that uses poer off the psu ie: usb devices new pci card ect any thing
when i built my freinds computer about 1 year ago it worked fine the first 5 months and then it started shutting off there are some components in the psu's that don't last long
other than that good luck
i had a problem to come to recall but it was due to my own stupidity the power cord for the pc was barly connected every time you bumped the desk just the right way bye bye all unsaved
