Don't those Packard Bell machines have recovery partitions on them?
If so, do you need an XP CD or recovery disk to access it? I really don't know myself.
As other people have said you can borrow an XP CD as long as you have the original XP serial number.
If you don't have the Microsoft number and you've lost your disc it's unlikely you will repair your system without buying another copy of XP.
And even if you do get a copy of XP it's very rarely that Windows XP is able to repair itself.
My success rate in this area: Zero.
If you have neither disc or number and your machine is capable of running Win 7 I would suggest waiting until October 22nd and buying a copy of Win 7 rather than another copy of the somewhat antiquated Win XP.
Good luck.