I've scanned for viruses, fixed my registry, and defragged...Why does my computer still run ver

I can especially tell that it's running slow when I try to run audio or video apps. It stops, stutters, and sometimes even crashes. I have somewhat of a powerhouse computer (Toshiba with an Intel DuoCore2. 1.5G of RAM. It's a year and a half old), so it should be able to handle simple audio/video applications. But even as I type, these letters are coming up very slowly. Another note is that the fan seems to have trouble starting sometimes. Any answers would be VERY appreciated.

I've scanned for viruses, fixed my registry, and defragged...Why does my computer still run very slow?photoshop

Make another user and log in. This is very easy to do and it works like magic sometimes.

I've scanned for viruses, fixed my registry, and defragged...Why does my computer still run very slow?symatec

If it is that new and already gotten that bad , then I would recomend a reformat and reload
Definitely do the spyware thing, then go to Start-Run-type msconfig in the box. Choose the Startup Tab, and go through the list of programs that run every time you start your computer. Uncheck anything you know you don't need to be running all the time. Then close the utility and restart your computer. See if that helps.
Did you do a search for adware or spyware, they both slow down your computer alot.