I built this system less than two years ago never had a problem till now. Shutting down at random, I deleted the hard drive, reformatted and reinstalled the OS once the installation reaches finalization the CPU shuts it self down. (Intel3.0,gigabyte ga-81848p775-g,1gig ram3200,450w Rosewill ap-500x,80g maxtor,4 fans...

Test the RAM first with a memtest program from dos.

I don't know why people think reformatting is the way to fix things. I doubt it's the RAM, but it wouldn't hurt to test it. More than likely the CPU is overheating (due to a bad fan or dust buildup) or your power supply is on it's way out. Rosewill is not a manufacturer, they're a "relabeler"...you may have gotten a good brand name PSU with a Rosewill label slapped on it, or you may have gotten a crappy generic unit. It's a crap shoot. Get the UL number off the side of the unit & enter it in the search box at the following site...it will let you know exactly who manufactured it: http://database.ul.com/cgi-bin/XYV/... Here's what the UL File number looks like: http://www.hardwaresecrets.com/full...

Failing power supplies are common and can cause your symptoms. Check your PS. See response 4 in this: http://www.computing.net/hardware/w...

ATNG POWER CO LTD is the name of the power supply?