I will assume you have Windows XP. If not, I have no idea how to help you.
Restoring your computer means erasing everything back unto a given point. You could restore to, say, yesterday, and everything you did today would be erased from the computer, including files, settings changes, etc.
Save everything you want to keep that was made or changed in the past... 3 days, to hard disk. This will ensure you don't delete something important.
Hit your start button, and go to all programs> accessories> system tools> system restore
Follow the on-screen prompts, and pick the date (or closest date) BEFORE you downloaded (and more importantly, installed) the program you're having troubles with. You CAN un-do this change if you need to, but this should get rid of your problem.