tune Xp i would leave alone for now click here
a repair install click here in my opinion will not be helpful to you, although you should not lose any data apart from windows updates it wont fix software or hardware problems.
"I now have the original with which my system was set-up by my neighbour."
do you not have your own original xp cdrom or restore disk/floppy? did your neighbour give you a copy of windows? and have you ever tried to update windows? click here