Sounds like you have install a program that had Malware.

get Malwarebytes Anti-Malware and avast and scan your Computer

and get and run CCleaner all 3 of the programs are free and work good


if that dont work just backup all your files you need and format you Hdd and just put windows 7 back in it (i do this ones every 6 weeks to keep my computer running good and fast