Have you got some anti-virus?? Although this free online one is better than AVG (sometimes) http://housecall.trendmicro.com
Run your AV, if it don't work, use housecall.
I also Suggest you get Spybot Search and Distroy, Ad-aware SE, Microsoft Defender, aswell as hijack this and see what they bring up.
That should get rid of it.