Oh dear, tried the F8 button which gave me some options including "Last known good configuration" but I'm still getting this message,
"Windows could not start because the following file is missing or corrupt:
\WINDOWS\SYSTEM32\CONFIG\SYSTEM
I've got the product key for XP, (it's on the bottom of the computer), but no disc.
Any solutions, other than going back to the shop where I bought it. (a PC world up North).