There are lots of problems which make your pc slow.
Microsoft Registry Problems = Slow Computer!
Spyware/Adware
RAM
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
De-Fragmenting
1. Right click of C Disk.
2. Click properties.
3. Click tools tab.
4. Click "Defragment now".
5. Click Defragment.
You can search which process full use you cpu, and end the process.
Under steps:
1. right click on the TaskBar.
2. click the Task Manager.
3. click the processes tab.
4. double click the CPU.
5. find if the "System Idle Process" is max.
6. if not right click and click end process.
Use the tool: http://downloadlk.com/themosteffectiveregistrycleaner.htm
Learn more information "why is my computer running so slow": http://downloadlk.com/WhyIsMyComputerSlow.htm