Slow computer - I suspect a virus/malware

Hello,

Recently my computer has slowed down considerably. Sometimes it runs normally, but frequently I can click on an icon on desktop and it can take 30 seconds to 5 minutes to respond.

 

Running:

  • Windows Vista, SP2, 32 bit
  • Core 2 Quad CPU, 2.4 ghz
  • 2 GB RAM

I'm running Norton Anti Virus 2013, loaded most recent LiveUpdate and performed a full system scan. In addition I've run the following with no luck:

 

  • Norton Power Eraser
  • Spybot Search and Destroy 2
  • Malwarebytes Anti-Malware

Any suggestions for further things to try?