How can i start my my laptop.when i try to boot it i get an error message?

The error message says windowssystem32configsystem is missing or currupt.i bought the machine off ebay about two years ago as refurbished from a reputable seller.it came with xp home preinstalled but with no other discs.i think it may have a partitiuon with the recovery/boot installed.i cannot start it in repair or safe mode,if i try i get a registry error message. i have a product key sticker for xp underneath the machine
Answer
Try pressing f8 repeatedly it should restart