What does "back to normal" mean?
If you mean 'back to the way it was when I first turned the computer on' you
need a set of recovery CDs or a recovery partition on your hard disk - check
with the computer's manufacturer. If you don't have either of those, you
can't return your computer to the way it was. You'll need to buy a copy of
Windows XP and you'll also need to buy copies of all the software that was
installed on your computer, and then reinstall everything from scratch.
"Performing a Clean Install of Windows XP"
http://www.microsoft.com/WindowsXP/expertzone/columns/honeycutt/02october07.asp
If "back to normal" means 'working properly again' you may be able to do
this without erasing your hard disk and starting over. The first thing you
need to do is to identify what program(s) are causing you problems. If you
think that Windows XP itself is the problem, you can try this:
"How to perform an in-place upgrade (reinstallation) of Windows XP
http://support.microsoft.com/default.aspx?scid=kb;en-us;315341&Product=winxp.
You might also try posting your specific problem(s) as clearly as possible.
Someone from this group may be able to offer a solution.
Rocky