First Update You windows press here http://update.microsoft.com/microsoftupdate/v6/default.aspx?ln=en-us
Then Try Download and scan Use Malwarebytes Anti-Malware:
http://www.download.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?tag=contentBody;mostPopTwoColWrap&cdlPid=10896905
Download, install, update and select Full Scan.
Remove all infections that it finds after scan.
SUPERAntiSpyware Free Edition:
http://www.superantispyware.com/
Download, install, check for updates, then select Scan your Computer, select your drive and select Perform Complete Scan
Then Try to install You anti-Virus.