Is the Windows 7 on your computer one that came preinstalled, or is it a retail copy of Windows 7 that you installed?
If it's a preinstalled Windows 7, then what brand is your computer, and is it a laptop or desktop?
If it's one that you installed, then doing a clean install will wipe the computer clean and put a fresh installation of Windows 7 on it. Clean Install Windows 7 Clean Install with a Upgrade Windows 7 Version
Hope this helps for now,