Kelvin, as asked by Soquili - what OS are you running?

In general, find where you installed the application - find the settings folder - delete the file. You can't find the application files at all? Show us the file structure you can find.

Worse comes to worse:

Clean up your scratch disk(s) (delete any nonsense files) and reinstall Photoshop. You shouldn't need to do this though as getting rid of the Prefs files should do the trick.

If a reinstall doesn't work... You have serious problems with a virus (or a few).

Risto