Try the usual pack of virus-killing programs: SuperAntiSpyware, MalwareBytes, Microsoft's Malicious Sofware Removal Tool. All of these can and should be downloaded onto and run off of a flash drive. If that doesn't work, you may have to reinstall Windows.
But after you eradicate the virus, there are a lot of other things you'll need to do to keep that from happening again. For one, make sure that you don't run an Administrator account (even with UAC, entering a password is a much better sanity check than clicking the Yes button). Install WOT into your browser (preferably Chrome, as it's the only browser with sandboxing as of now). Maybe even the new Noscripts extension for Chrome if you don't mind the timesuck it takes. Install an anti-virus program (Microsoft Security Essentials is fine) before you get a virus. Back up your stuff. Don't disable Automatic Updates. All that fun.