If you suspect a virus, then try this free
web-based scanner and see if it detects anything. Do you have any reason to suspect a virus?
You might also want to tell what you have for
1) Operating system (Win2000, WinXP, whatever)
2) Service Pack (SP2 for WinXP, SP4 for Win2000, etc)
3) Hardware firewall (Linksys BEFSR41 router or etc)
4) Software firewall (WinXP firewall, ZoneAlarm, etc)
5) Exact brand and exact version of your antivirus software
6) Do other people ever use your computer
7) Do you use a full-blown Administrator-class account for everything (if you don't know one way or the other, then you are using an Admin account)