Ordered a new PC which came in yesterday. Played on it for about 16 hours then did a windows update before going to bed. Comp failed on the restart and would shut off after about 2 seconds. Now it will just turn on and off on its own. On for 2-3 seconds off... on again by itself then off etc.. I've checked all the cables unplugged/plugged back in, moved ram. When I took the mothoboard battery out to reset the CMOS it booted up again normally and worked. I then restarted just to make sure it wasn't a fluke and it failed on the restart again and is now doing the same problem on/off every 2-3 seconds.
I got this computer from cyberpowersystem.com
Neither is likely to fix your problem, as it is rebooting before BIOS it is a hardware problem. I know I have the same issue. I managed to fix one PC with this problem by disconnecting everything and cleaning each part, some people have associated this problem with dust buildup.