HELP!!!!

I have managed to crash 2 computers recently. One of which was a BRAND NEW laptop that we just got last friday. Everytime we use a search engine and click on a page it redirects us. Also, we have this thing that will pop up saying something along the lines of "Your computer is infected, check for viruses" and a fake virus scan will come up. We took our new computer in to best buy and it was so messed up they had to give us a brand new one. And, they said they thought it was virus I was getting through my facebook (say it ain't so!)!!! Anybody have any advice? We have an antivirus- webroot. Anybody got anything???