You can try this:

- download and install Malware Bytes (a highly rated anti-malware software) from here:
http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?part=dl-10804572&subj=dl&tag=button

- re-boot you machine in Safe mode (as you re-boot keep hitting F8, at some point you will get a menu of options, choose 'without networking')
- you will get windows with all these warnings that you are in safe mode

- run the software.

I once had to run the software and re-boot 3-4 times, but it finally got rid of it...

Other free software you may want to try are:
- Spybot Search and Destroy
- Ad-Aware (from Lavasoft)

Good luck!