Can someone help me please before i throw the pc out of the window <desperate>

[MasterDebater]

The computer has had a virus and it fooled itself into believing that our windows xp thing wasn't real so we can't log in etc. We have borrowed a xp disc from a friend but the code on it is coming up invalied. Its an xp pro upgrade serial number that i think we need but i've tried googling and no luck. Please does anyone know anything about this? Please?

Do you have a sticker on the machine with your serial number? You might have better look using that as Windows Genuine (dis)Advantage will have logged that the serail number on your friend's disk has already been used.

Alternatively, do you really need Windows? Ubuntu is free and comes without all this validation crap.

I should add that while you're trying to sort out Windows you can always run Ubuntu in "Live CD" mode, which doesn't install it onto your hard disk, so it's quite a safe way of trying it out. It will allow you to use the machine for web surfing, but it will be slow because the CD player is a lot slower than the hard disk.