Computer slowdown.....

I'm totally flummoxed so lets see if any of you guys have a solution...
First of all, I have been having lots of computer slowdowns as of late. This mainly manifests itself with the mouse lagging for about a second before responding to a click, mainly with the start button and various windows. I'd say it was a heat problem, except I have just left my computer cold for about 4-5 days, and it has done it right on startup. I don't appear to have any viruses, both adaware and spybot say I have no spyware, and none of my processes look out of place....
What else could be causing this???

I would say to go to blackviper's site and do some service optimizing, but it appears to be gone again. Depending on the age of your PC, it's probably just getting a little cluttered, both soft and hard.
1) Clear dust from your case, check to make sure all cards and RAM are fully seated, and make sure the bearings on your fans are running well. If you need a fast way to clean dust, grab a friend that has a moisture-free industrial air compressor and hose your PC and PSU.
2) If you have an optical drive, make sure it's on its own IDE channel, or at least not slave'd under a HDD. If you have no clue what I'm talking about, ask  your friendly local geek.
3) Grab some optimization tools better than the crap stock M$ supplies. NTREGOPT to sort and defragment your registry and Diskeeper as a much better disk drfrag. If you know how to tweak your PC without hosing it, www.freshdevices.com FreshUI can help speed the tweaking process and it's totally free.
4) Less HDD space = less performance. Get rid of as much stuff as you can that you don't need on your boot volume. If you have multiple drives, move stuff from your system drive to another. If you're on AOL (god save your soul), see if you have 7 billion copies installed and get rid of them. If you know you're never going to uninstall a Windows update, you can safely delete any $NTUninstall folder in C:\Windows and free up quite a bit of space. Also, when you uninstall things, empty folders and small files are often left behing. A good scrubbing for such things helps by clearing out unnecessary file references.
5) http://www.tweaktown.com/ hase some good optimization guides that go into depth where I'm too lazy to type.

I know these are pretty generic, but they ought to help.