It must have been virus infection.
You should try to boot the computer in safe mode, and see if the PC works properly. If yes, then you can run system restore from the safe mode. When you boot into safe mode, it gives you option to run system restore, or to run PC in safe mode.
The system restore exe as told by Jojoyee resides in C:\windows\system32\restore folder. So, you can run from there too, by navigating through command line.
You can also run virus scans if the PC does boot up in safe mode.
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Anupam
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