"system32\system\config was missing or corrupt. Found a registry repair on the internet but although I could reboot a lot of the programs no longer worked correctly."
Takes the config file from the XP CD and replaces the corrupt one, unfortnately everything you have installed is nolonge registered. Had this regular on my old PC so started to copy the config file on a regular basis so could rest a little like system restore.
"Anyway, this morning when I turned on the computer it keeps restarting, windows will not load."
Sounds again like a simular problem a corrut system file.
What if any eror message?
Run check disk from recovery consul.