In your situation, there are a few options you can choose.
1) Reformat your hard disk and reinstall your Windows, which you can leave it as
a last resort.
2) Take out your hard disk and install as a secondary drive in another PC that
have a good anti-virus program. Boot up on that PC and scan your infected hard
disk.
3) You can install Clamwin anti-virus.
ClamWin is a Free Antivirus for Microsoft Windows that uses the GNU General
Public License by the Free Software Foundation and is free (as in freedom)
software. It can detect and remove more than 400,000 Trojans and viruses.
There is a portable version of ClamWin anti-virus where it can be install into
an USB pen drive as small as 64 MB.
First, you use another PC to download Clamwin portable anti-virus
and install Clamwin portable on a USB pen drive.
Download here
http://portableapps.com/apps/utilities/clamwin_portable
Start Clamwin anti-virus and update the latest anti-virus definition files.
Select the tools menu bar, set the preferences to remove virus.
Document on how to configure ClamWin
http://support.real-time.com/open-source/clamwin/index.html
When the USB pen drive is ready to be use.
Start the infected PC in safe mode by pressing F8 during start up.
If possible, disable system restore on the infected PC.
Run the Clamwin Anti-virus that is installed on the USB pen drive to scan the
infected PC.
After removing the virus, install crap cleaner (ccleaner) to get rid of the
viruses left over setting in the windows registry.