Windows XP Pro +SP2 Repair Re-Installation Fails

Can anyone please help. I have tried to carry out a Repair Installation but when Windows first reboots after loading all the files, it reaches the Logo screen (with the scrolling bar) and then just ‘Hangs’ indefinitely. After that I can no longer boot-up at all, it just takes me to the Logo screen again and guess what – it hangs again.
I have a lot of data on my 300GB HDD which I don’t want to loose otherwise I would do a ‘Fresh Install’. An earlier problem I found when I tried to boot-up in ‘Safe Mode’ was that after it had finished loading the drivers (the last one being ‘Mup.sys’ again it just hangs. I don’t know if the two are related but this is what prompted me to do a ‘Repair Re-Install’ Any ideas anyone (I have 2GB of RAM installed).
Thanks, Bob