If you suspect that your PC is infected with some sort of virus or malware try the Free F-Secure online anti-virus scanner. It works only with Internet Explorer but is an excellent scanner that pretty much caught everything in my PC that other scanners missed.
Here is the link:
I would suggest running this can along with atleast 2 more anti-virus/malware scanners such as AVG (Free Edition is fine) and MalwareBytes. Leaving the scanner to run overnight is a good idea as the process is time consuming.
AVG Free Anti-Virus