First thing i would do is make sure that you have all of the microsoft patches installed (don't install sp2 until this issue is fixed if you havn't allready)
next i would verify that the virus scan results are correct. go to
www.mcafee.com and select home user. there should be an option for a free scan over the web that will tell you if there is an infection.
then i would clear all temp files by going into internet explorer, select the tools menu and select Internet Options. Under Temporary Internet Files click delete files (include all offline content). then i would also delete cookies (will require you to re-login to sites that you frequent). close internet explorer and then re-open it and try the site.
let us know if that makes a difference.