If you want to repair it as Pro, you'll need the product key and a genuine MS CD of the same type used with the installation. Because you said it was originally XP Home, shall we presume you used an XP Pro "upgrade" disk? That would be normal route to go from Home to Pro. If a full version was used, it would likely have been an OEM or retail copy. In any event, the repair installation will only work with your product key if you have the same version of XP. If you can't do that, your options would be a clean XP Home installation or the purchase of a copy of XP Pro of the right version for the repair or even a clean installation with it.
I start my pc which runs xp pro edition, originally home edition. When it starts, the xp logo comes up with the scrolling bar below it, but afterwards the screen goes black. I read other places that i should try to repair it using a windows disc, but the only disc i have now is the home edition, can i use this disc to repair it. and will i need a windows key(which i no longer have due to roaming babies)?