Please state the exact error message without paraphrasing for the forum to more effectively help you.
Update your antivirus, temporarily disable your screen saver (choose None) and scan with your anti-virus set to scan All Files. Update and scan bi-monthly.
You can scan on-line to double-check your Windows scanner at
http://housecall.trendmicro.com/
*** Mandatory (get a firewall of any brand) - Get free Zone Alarm personal firewall anti-hacker countermeasure from
http://www.zonelabs.com. (not the ZA Pro demo) 'Don't let anything out to the Internet you don't know what it is.' Also please see
http://www.firewallguide.com/ for more information on why all on-line home computers should be firewall enabled.
Get the firewall if you have none, then do on-line scan.