Pc lagging , slowing down noticeably

My pc was ok , just fast and ok , suddenly it started slowing down really good and responses became so dull that windows stopped responding and had to either wait till it responds or restart windows 7 . I downloaded a game called blur and the game launcher .exe was some kind of a malware or Trojan. I scanned my pc and removed two files via Avira anti-virus from the local disk c . Then I made a clean installation of windows 7 again but the lag is still there and responses are still lagging and very slow . I tried cleaning the case with air , might made a slight small change but the lagging comes back and is still there . I want to ask , is it a virus thing, hardware thing, software I doubt since it was working fine and after the clean installation no difference . Mayday mayday ! Man down people

 

If this is a fresh install, there's a good chance it's running slowly because it's downloading a lot of updates. I'd advise you to have a look at this thread, which will help you get your machine up to date.