Go to Start> Run> type "msconfig" then go to the "startup" tab.
If you see it on the list, then disable it, if not, then you may be infected.
I fear that you may have TROJ_VB.CST trojan.
Also, tell me, after startup, or at any time during use, do you have a process under your "processes" tab in taskmanager (ALT CTRL DELETE)??