having purchased my pc it had xp pro pre installed and one of my kids has played around with it so much that it wont let me do a system restore to undo the changes and wont even do a disc cleanup i cant find my coa or number to contact microsoft for help can you help to repair my problems ..thanks

I know it might sound obvious but have you ran virus and spyware software? I only ask because i've had a look at some of my friends pc's when their machines have been acting-up and they've assumed it's their kids, changing setting etc, when actually their comp has become infected...
Try running AVG & spybot s&d (google them both for free downloads) and see if you still have the same prob.

What exact problems are you having?

What is the make and model of the computer?

Do you have your XP Recovery CD?

can u recommend a good free xp pro repair download appart from microsoft help ....thanks

what problems are you having?.

have you tried a repair installation?