Your operating system would sure help here, (If XP, which Service Pack?) but please try the steps in the links below. It should help clean things up a little.
For Windows 2000/XP, ignore the first couple of sentences about checking "resources" in the link below but follow the rest of the procedures including the "Services" links at the bottom.
How To Shut Down Unnecessary Start Up Programs
How To Clean Unwanted Files From The Hard Drive
After following all the procedures above, if you're using Windows 2000 or XP, run Error Checking/Chkdsk and Defrag to optimize the hard drive:
How To Run 'Error Checking/Chkdsk' On Win2000/XP
Hope this helps and let us know how it goes.
Grif
I have had this PC for 18 months with no problems, but yesterday my computer started stuttering and I was unable to run certain programs without severe lag!
I checked the CPU usage in the Windows Task Manager and am finding it to average around 70 to 80%, even when I don't have any applications running.
I rebooted in SAFE mode to see if this still occured and it did.
I have used Ad-Aware SE, spydoctor, spybot to check for spy/ad ware and I seem to be ok.
I also have Norton System Works and ran the basic scans.
I have no clue what I should do/try next.
I wanted to ask u guys, before I do something damaging to my PC.
If anyone can help, please let me know!!!!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic