|the best free antivirus is Avast Free:|
i've been using it for almost 10 yrs, knocks the heck out of almost all the others because it has the best real-time protection and automatic updates daily and you don't need any scheduled scans.
I've use Trend Micro, AGB, Avira & some others and Avast has proven to be the best. I install it on all the repairs that I do.
Now for your problem, you can try Malwarebytes, update it and run a full scan to start with.
Is your windows 7 32 or 64 Bit?
Some HELP in posting on Computing.net plus free progs and instructions Cheers