1. An overheated processor will do such.. Remove the heatsink, then remove the old thermal paste, then reapply a new, THIN covering of paste to make sure the heat is being transferred correctly from the processor to the heatsink.
2. If you haven't done so, make sure you check the manufacturer's websites for the latest motherboard.chipset drivers, plus all other drivers, and possibly the BIOS update for Windows 8 and all installed hardware.. In some cases, it can be as simple as an updated video driver for Windows 8.
3. You've not mentioned the power supply.. Tried swapping in a different, known good power supply?
Hope this helps.
I just built a new desktop PC with specs:
Geforce GTS250 DDR3
Hynix DDR3 2GB 1Rx8 PC3 10600U (HMT325U6BBFR8C)
The Pc been doing fine for a month or so. and suddenly it just keep rebooting even before it gets into the bios (it wont go the bios even if i keep pressing del)
If i just let it run and keep rebooting it will eventually get into the windows. but lately the rebooting sequence would run for the whole day.
There are no error with the RAM when i check it with windows memory diagnostic tools. The VGA also works well if i plug it into my other computer.
I've also check the motherboard with the service center, and there is nothing wrong with the MB.
is there anything else i should check?