There are lots of problems which make your pc slow.
Microsoft Registry Problems = Slow Computer!
Spyware/Adware for your use another software to scan
RAM you've increase it.
De-Fragmenting
Etc.
Below can help you speed up your pc:
From IE, click Tools, Internet Options delete cookies delete files (offline files) clear history (set days to save to 0 if you want) click o.k., and Restart
1. Quit Internet Explorer, Firefox, or any other web browser
2. Click Start, click "Control Panel", and then double-click "Internet Options".
3. On the General tab, click "Delete Files" under Temporary Internet Files.
4. In the Delete Files dialog box, click to select the "Delete all offline content" check box , and then click OK.
5. Click OK.
Manage your startups. Your excess CPU usage is due to too many programs running in the background. You can cut these to barebones by alter your msconfig. Here is how:
1. Open your Start menu.
2. Click Run
3. In the command screen type "msconfig.exe"
4. In the "system configuration utility",click either "service" or "startup" tab
5. Uncheck all programs that your are no longer using.
6. Click "OK"
De-Fragmenting
1. Right click of C Disk.
2. Click properties.
3. Click tools tab.
4. Click "Defragment now".
5. Click Defragment.
Use the tool: http://downloadlk.com/themosteffectiveregistrycleaner.htm
Learn more information "why is my computer running so slow": http://downloadlk.com/WhyIsMyComputerSlow.htm