Here's a way to clean about 98% of dirty windows systems, I personally use it on people's pc's most of the time there are viruses/adware/trojans present without the need to find a specific virus fix/patch for it (because most of the time if there is one there are others).
Run these one by one, making sure to reboot your pc between runs (also do these steps in safe mode, without the adware being locked by the system):
First download and run VundoFix (click remove Vundo when done, alot of spam sites use it):
http://www.atribune.org/ccount/click.php?id=4
Then download and run ATF Cleaner (check all other than Cookies and History):
http://www.atribune.org/ccount/click.php?id=1
Then download and run Dr.Web CureIt (start it, let it autoscan, then when it's done click Settings>Change Settings>click Actions tab and under Malware set everything to 'Delete' click Apply and OK then start the scan (click the green play '>' button), it'll scan and auto delete all malware for you), this is probably one of the best virus cleaners for windows if regularly updated (which also removes rootkits):
http://www.freedrweb.com/
Then download, install and run SUPERAntiSpyware (when done you can choose to uninstall it):
http://www.superantispyware.com/