Since you can't get into Windows, if your friend permits you to piggy back your disk into his system, you can use his computer to scan your disk for viruses depending on how uptodate the virus program is. You can also download a Virus Stinger for free from McAfee use it to clean your disk too. When cleaned remove to disk from your friend's PC and put it back to your PC, if all else fails you might have to rebuild and please use anti virus software.
Kim