Computer isn't running any programs...

Alright so my computer had a nasty virus a couple of days ago, I downloaded and ran Spyware Doctor and it got rid of the virus. But that same day I went to listen to some music and tried to open iTunes and after waiting for a couple minutes it wouldn't open. I checked the task manager and it showed iTunes as running. I also tried this with Firefox and the same thing happened. It doesn't happen with all of my programs though, I can use everything is Windows just fine. Sometimes when Firefox does open it can't access the internet so I can't download anything to that computer (I'm on a different computer right now). The same thing happens with Internet Explorer and Google Chrome.

My computer is a Gateway running Windows Vista with the 32-bit operating system.