Update your Anti virus definitions if you can. It will probably fail. Then do a full computer scan in SAFE MODE:
1. Enter safe mode by tapping F8 as soon a the computer starts or restarts. You will get a menu to enter safe mode, try safe mode with networking as then you might be able update your AV definitions.
2. Do a full computer scan while in safe mode, delete or quarantine any nasties.
3. Reboot and do it all again, enter safe mode and do a full computer scan.
4. Reboot into normal mode. If the virus comes back then you will need to work harder to clean it up. Tools like Hijackthis will help but are not for the novice. Get a nerd buddy to help or otherwise backup your files, bookmarks etc and wipe the machine.
Good luck