Ok, you're going to have to help us out a bit here as there are many reasons why a computer would run slow besides malware. In an effort to try to narrow this down a bit, did you recently install any new software or hardware? Do you get any error messages? Anything you can tell us may be helpful.
Download
combofix from one of these locations:
**Save it to your desktop**
Double click on combofix.exe & follow the prompts.
When finished, it shall produce a log for you. Post that log in your next reply
Note:
Do not mouseclick combofix's window whilst it's running. That may cause it to stall