My PC has started shutting down on it's own.

In the past month I upgradged from Windows 8.1 to W10. It all went well but now my PC has been shutting down on it's own. In my honest opinion, it can't be hardware since it has been happening since the upgradge, but there's something going wrong and causes my PC to shut down at random (Some times it would shut down after an hour of running, now it shut down before the computer even booted in W10). The temps seem fine (and ofcourse can't be temps since I just mentioned that it shut down before the boot), HHD seem fine and I haven't checked the CPU (Intel Xeon E3 1226 V3), the Rams (cant remember the model but are 2 sticks of 4x4gigs) etc. My PSU is Thermaltake Smart Se 630w and hadn't caused me any problems when I was on W8.1 . Is there any problem with my W10? Could it be my hardware and could the problem coming after the upgradge be coincidence? How could I check it? Thanks!

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