Pc slow for a lot of reasons.:
Spyware,Temp files,Defrag,Disk cleanup,Virus,Bloated Operating system......

Here's some steps that might help:
1. Check for viruses/malware
http://www.safer-networking.org/en/download/index.html
Download, install, update and Immunize, then click 'Check for problems' then when complete select all and then 'Fix Checked'

2. Check what applications are starting up when you boot your computer (start->run->msconfig then take a look at the "startup" tab). Anything listed here will start up with your computer. Some of these things are necessary, but a lot are related to applications like QuickTime, Java, Nero etc. These things will run in the background and use up memory and CPU time.

3. download Perfect Optimizer and run to remove temp files.
http://www.Easy-Registry-Clean.info

4. Uninstall any applications you don't use/want.

5. Defragment your hard drive. (usually start->All Programs->Accessories->System Tools->Disk Defragmenter).

I have a 9200 and after upgrading to SP3 I've expereinced huge slowdowns, and some display weirdness. Let me know if you figure any of this out