1) buy an antivirus if you don't have one (you could also download one, but are we allowed to post illegal stuff here? xD)
2) scan your computer with the antivirus (deep scan is the best, also scan cookies and trackers).
3) if you have found any trojans, delete those immeadiately, any other virusses as well of course
If your PC doesn't do anything anymore (you've got that with some virusses :/), you need to defragment it...
Meaning you need to erase everything on your PC.
This always works, but of course it's not really funny... I suggest you copy all files that you know that aren't corrupted on an external drive (I've got a 1TB external hard drive and 2 16GB USB-sticks, for example... I could easily put everything on those).
Antivirusses I recommend:
- BitDefender
- Kaspersky
