Ok i have two errors. One is if i try load up my computer i get an error (not a blue screen of death) saying that a file \Windows\System32\Config\System is corrupt or missing. Therefore to try and fix this i have gone to XP install and selected repai on the 2ND menu screen not the 1st and i get a blue screen of death saying Bad_Pool_Caller. Please someone help me as i need my computer up and running as soon as possible as i need to do some Coursework asap. Please Help!

You could try this:

How to recover from a corrupted registry that prevents Windows XP from starting

If that doesn't work try a Repair Install as seen here:

How to perform an in-place upgrade (reinstallation) of Windows XP