I reformatted the machine (using an xp pro cd from a friend) when I enter the CD key it says its invalid
Was your original program Home or Pro? yo cannot use a home serial no with a pro disk.
My friend gave me an XP key which enabled me to finish the reinstall but now I cant install SP2 as it says my key isn't valid.
It will be installed on his machine and is therefore invalid on yours as well.
one license one machine.