Did my computer get a virus?

I opened up a message board that I regularly use and about five minutes later, my Internet closes this security thing pops up and it's not my anti-virus. I tried opening up my anti-virus and it won't come up. I restart my laptop and I do a disk consistency check and that's fine, so I go to my user and I finally opened up my anti-virus but the strange security check thing over-rides it and shuts down my anti-virus. At the moment I have my laptop shut down. What can I do?