Hmm.. laptop.. many ways to go about your situation.. BEST, is to pull your HD and put a new one in (saves your old information)..
OK... Just to let you know, you do NOT have to buy NAY Linux OS.. and Anti-virus options are always there.. but I have never had to use one (yet).. (and I have been on computers since 1980.. there are a few here that have been on them before me....)..
I got my first one in 1976....