Restarting Pc problem (no BSOD)

I have been trying to solve this problem for all week now.
It's new PC, specs:
MB: MSI B75MA-P33
CPU: i3 3240
RAM: DDR3 4GB
HDD: 500GB Toshiba
other: SATA DVD drive, 300W PSU. Intel's integrated VGA is used.

It came with windows 8.1 64bit pro. I tried installing backup software (macrium) and system restarted.
Then it started restarting at random times installing software, just changing settings and even when system idle.
No BSOD (I set to not to restart automatically when system crashes and to show BSOD).. in event log there is no serious errors except for Kernel-power id 41 system hasn't shut down properly.
First, because there is no BSOD I thought its hardware, most likely PSU so I replaced it with working 400W PSU.. nothing changes same problem.
Then I decided to test RAM I boot from memtest86+ boot cd and run it for more than 12 hours (33 passes) no errors no restarting..
It seems that pc only restarts when OS is running so I clean reinstall windows 8.1 same problem.
Then I do clean windows 7 pro 64bit install same problem.
I boot Linux from boot cd and there is no restarts as it runs from cd so I think it may be HDD.
Replace HDD with working HDD and do clean windows install and guess what same problem.
then I try replacing SATA cables no help..
I'm at loss here anyone can give any suggestions?

Try the Linux live. Mount a partition from the HD. See if that triggers the error.

Update after success with knoppix Linux I decided to try
Linux mint 16 cinnamon 64bit and system crashes/restarts during install (almost same as windows 7 and windows 8.1 difference is only that windows sometimes finish install process ok and crashes while running, but mint always crashes during install)

Now I'm thinking what is different. I'm not Linux expert so I don't know how those distros different. the only thing that I can think now is that I installed knoppix from cd and mint is on dvd.

Hmm maybe I will try to install windows XP next.

and again Update: Installed windows xp pro sp3 32bit everything looks ok so far no restarting.. what is going on :/
What to do next.. I think I will try to install windows 7 32bit
Anyone has any suggestions please?

It sounds to me like something doesn't like the 64 bit OS. Be it Linux or Windows. From your post it sounds almost like Macrium triggered it by turning on hw virtualization or something. I'm not enough of a PC hardware guy to know how to test the CPU. Maybe a system builder will chime in.

But the common theme in your last tests seems to be it doesn't like 64 bit OS.

I suggest you check you CPU settings and configurations. Check its the frequency is set too high in the B.I.O.S which will cause your system to hang which might be the cause of your system restarts. Try downloading CPUID software and check if the cpu temp matches in the correct temperature range.

Best of Luck.