[Hardware problem] Random reboots and freezes

Hi everybody,

some months ago, I built a new entry level PC for my parents. This was the set-up:
PSU XFX 450W Pro450S
Cpu AMD A8 5600K HD7560D 3.6GHz FM2
Mobo Gigabyte GA-F2A88XM-HD3
Ram DDR3 Crucial 8GB / 1600Mhz Ballistix Sport

The PC, even though never used under stress conditions (internet or office applications), has since the beginning had random reboots, both in Windows (after a BSOD) and outside (during the boot or even when in the BIOS menu).
I initially thought that the problem was the motherboard, since I also got random "bios corruption" errors at boot.
So, even if the shop said they tested the mobo and it worked fine for them, I switched to a new one (MSI FM2-A75MA-E35).

After the switch, the PC seemed to work fine for the most part. At the beginning, there were few reboots (without BSOD) in Windows, but I wasn't there so I thought that might be a software problem. After a while, also those few reboots disappeared (at least my mom says so) and for a few months the PC seemed to work fine.

Unfortunately, in the last few days a new (?) problem came up. Randomly, in windows or in the bios menu or even during the boot, the video signal just goes off and the monitor goes to sleep. The fans keep working but, apart from that, the PC looks dead (ctrl+alt+del doesn't work, the caps/num lock indicator lights switch off and don't work any more, etc). I just have to manual reboot the PC and, sometimes, even that doesn't work and I have to manually switch it off and on again.
The problem seems to occurr more often when using cpu-intensive applications but, as I said, it occurrs even when in the BIOS menu. The other strange fact is that sometimes the pc works fine even for a couple of hours; at other times, when the problem occurrs, it just keeps coming again and again and the pc freezes few seconds after each reboot.
I cannot even understand if the problem is due to the same hardware failure as the first problem or if it's something new.

This is the Windows log file after one freeze occurred while in Windows (but I don't think it will help):

This is what I tried:
- I updated the mobo bios and the cheapset drivers
- Ram test (memtest86+). I first did it when the first problem occurred and the test was ok. I also tried to use a new ram stick but it didn't help. In the last few days, I tested the ram again. The first time the PC freezed as usual after few minutes. The following day the test went on for a couple of hours before the PC freezed. In all these cases, before the PC freezed, memtest didn't report any error.

I think that, excluding a software and a memory problem, the remaing available options are:
- PSU: these are the voltages reported in windows by the MSI utility (on the right) and by Hwmonitor on the left, whilst running a CPU-stress software. As you see, Hwmonitor (and Speccy as well btw) reports strange values. The ones reported by the mobo utility (which are the same as the ones I get in the BIOS menu) seem ok to me. Which ones are the right ones?


- overheating CPU: as you can see from the same screenshot, also for the cpu temp readings I get a huge discrepancy between hwmonitor (and speccy) on one side and the mobo utility (and the BIOS) on the other. Anyway, I don't think overheating is the problem (sometimes the problem occurrs just after a cold start-up).

- cpu failure

- mobo (again???)

Any ideas?

Thanks a lot.