If the computer runs at all, copy all your data files to a cdrom.
Then wipe the hard disk and reinstall the operating system. Then
install new anti-virus,
then and only then reload the data from CD.

Better yet, run Mac or Linux.

There will be a Mac/Linux virus someday. But it hasn't happened
yet, not installed through the browser anyway. There have been
some "virtual machine" hacks that have leaked into Mac,
but nothing yet that installs just by visiting a website.