Hi,
please read the link "VirusRemoval" below in my sig and:
- post a hijackthis-Log for diagnosis
- tell us exactly WHAT virus was found WHERE (full path/folder filename)
- report the results of Onlinescanners and of updated avast
- tell us what Win you have and whether all Windowsupdates are applied
you can try repairing your IE-Browser via ControlPanel -> Software -> InternetExplorer -> uninstall -> repair
but this should be tackled after the PC is cleaned