On my custom built computer, I've had a issue where it randomly reboots on me. No blue-screen, just black then it reboots, almost like if you kill the power.
I bought a UPS, thinking it might be house electricity that was unstable. Still having the problems.
Today it died on me but this time it didn't reboot. Pressing the power button a few times didn't do anything. Checking the power connections, I moved the power cable to another outlet port (these are battery backup and surge protection outlets on the UPS). It rebooted.
A little while later, I tried using the original outlet port to charge my phone. It works fine.
I'm thinking of getting a EVGA or Corsair 750W Bronze and hope that helps.
P.S. Or maybe I'm haunted. The other day, the overhead lamp bulbs died on me.