dclary said:
#1 cause of slowness on any computer I've ever seen is Norton Antivirus. What a resource-sucking piece of sh*t that is.
McAfee always bogged my system way down. Norton not so much. BitDefender was pretty good, and actually found a virus on my machine when Norton couldn't.
As for the original question: I would check for spyware first. Adaware SE is a pretty good freeware setup, as is Spybot Search & Destroy.
Another thing that I might mention is your Internet browser. Have you cleared your cache and your cookies? Enough of that stuff accumulated in your computer can really slow it down.
Also, be sure to use the maintenance features included in your operating system, such as Disk Defragmenter, etc., about once a week. My piddly little 500 Mhz Compaq Presario desktop works pretty darned good when I keep up the maintenance on it. It's slow, but not as slow as it could be.
One more thing: what operating system are you using? If you're using a newer system such as XP, it uses a lot more memory than does, say, 98SE--which, BTW, Microsoft quit supporting with new updates on July 11th. If you are using a big system like that on an older PC, you could have some problems opening things up because of the resources needed to run your OS.