My PC restart at 6 am - 9 am while playing games, and if it's not playing games, pc didn't restart

[juen juariyah]

I have homebuild PC, here's my spec

AMD A8-6600k
PSU >500 watt
Cooler master 212
kingston 4 gb ram
1 TB WD HDD
Onboard GPU
MB GIGABYTE F2A58M-DS2

when playing games (online/offline) every 6 am - 9 am my pc always restarts, and doing fine after that "interval" . 6 pm- 6 am, nonstop gaming, my pc never restart. And if i did not play game, every 6 am - 9 am pc never restarts, i don't understand the problem of it, i did swap my Proc with my brother and still restarting, change RAM, no change. i installed HMVmonitor and my tempt show normal about 25-30 then 27 degree. i also disable autorestart from windows 7 and no Bluescreen. please help me.

Thanks
Juen

Sorry for my bad "english"

 

[rgd1101]

could be a load on the circuit. 6-9am is about when people get up to go to work.
what the make and model of the psu? using a ups?

 

[juen juariyah]

that's what i thought. my PSU ATX non modular. oh and i did not use any ups.