Computer Restarts on it's own

Okay, so here's the story. 2 days ago my computer kept opening up a DOS window. I searched the web and it was a virus, so after trying to remove it with various programs and failing I decided to do a complete hard-drive format. Did the format, reinstalled windows. But I seem to have traded one problem for another now, because Windows will just either shutdown or restart at random intervals. When it starts by up, or reboots i get the whole send error report thing, that windows had recovered from a serious problem. Now about 4 years back my sisters computer kept doing the same thing, but with her it was a power supply isssue. She had to get a brand new one. I'm I faced with the same problem? Or a complete new one? Thanks very much.
 
What exactly is this restarting computer's specs? A new power supply sounds good to me, since you have already done an OS reinstall... Turn off "automatically restart" under System, Advanced, Startup and Recovery, settings
 
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