Computer restarts randomly

Hello. My computer has recently started to restart randomly. Screen instantly becomes black, and after around 10 seconds computer starts booting again. The computer is running all the time during the process (no power loss). By the way, normal restart takes 2-3 seconds of "black screen". 3 days ago i got 5 crashes 10-15 min after turning computer on. 2 days ago i did not have any (i cleaned computer inside and changed the extension cord). Yesterday i was using computer for very long time without any kind of problem, so i thought it was the cord problem, but this morning i had 4 the same crashes, each after~5 min after boot. I unticked the "reboot after error" - still reboots.

I am not getting BSOD, event veiwer says only:
"The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly."

There is no minidump, i unplugged and plugged again ram, disk, graphic card, ran disk check and ram check.
CPU/GPU temperatures are 35-45. The northbridge is hot, but from what i read, it is normal temperature. The motherboard and gpu are new, 6 months since i bought em.

BIOS voltage shows 3.363, 5.190, 12.168

I've got no idea what may be wrong. The lack of any kind of crash information makes me completely confused.
Thanks in advance for advices

The good folks here will need your system specs.

This tutorial by Brink should help you.
System Info - See Your System Specs

By chance have you been monitoring your system temps?

It would be handy to have the proper system specs.

WDC WD50 00AAKX-001CA0 is not a PSU. It's a hard drive.

Take a look at my system specs. I will give you a idea.

Temperatures are between 35 and 45. The fans are working properly, cleaning every component was the first thing i've done before posting.

Edit: This morning got 5 crashes after less than minute from windows start each. I rebooted in safe mode, and i am working without any problems. Should i reinstall all drivers then?