when was the last time you updated your comp? Are you running any Anti-virus? Do you have a firewall.
If no to updated or don't know, ya need to keep up with it. There are so many things floating around the net now that if you slack behind on an update, you'll get hammered.
If no to Anti-virus. Do a quick scan at
http://housecall.trendmicro.com. Then after, go out and dl a virus scanner such as AVG
If no to the firewall, you can use the free edition of Zone Alarm and you'll be better off then you are now.