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

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. 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'

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

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

If you have other problems, you can contact me at any time and I am pleased to help you.
My Email: lemon0angle@googlemail.com
My Msn： lemon0angle@googlemail.com
Good luck

I've noticed a real tendancy on the net to overthink these problems.

My very first step would be to go to Add/Remove programs in Control Panel and uninstall I.E.8. If I recall correctly, you'll revert back to I.E. 7.2 after a reboot of the O/S.

Just see if your Internet back to speed then. Odds are around 75% that this will fix the problem (in my experience).

Sas