Jonathan_108 :
My computer restarts randomly. No blue screen or like that. I bought recently new PSU Corsair VS550 so it should not be the reason.
The first question in solving any computer problem that suddenly pops up is "have you made any changes lately".
Since you changed the PSU and the problem popped up, it would be safe to assume that the new PSU is the most likely culprit. Just because it's new doesn't mean it can't fail or have problems. Put the old PSU back (if it's still working) and try again.