Joe has a good suggestion.
If the last know good config doesn'y work as you have already booted to the windows screen. Then have you tried pressing F8 and loading safe mode?
This will load up the most basic version of windows and from there you can try and sort out the problem.
When working on such a problem have a pen and paper make notes of everything you do and see. Will help you later on.
If you can load in safe mode see if your cd drive works then download anti virus and spyware removers. Then see what you can do.
If you just want the pc up and running have you a back up? Failing that do you have xp disk or a system restore disk which many pc firms supply instead of a xp disk.
Good luck
