Before you do anything else: do you have a backup of your data on the XP partition? Save your folders first!
Get any Linux "Live CD" (for live Mandrivia look at: http://www.linuxcentral.com/catalog/...=C1Cm2CeFly2CR
Boot from it, and with any luck it should recognise your XP disk and allow you access to your folders on it.
Once that done, you can start diagnosing the XP booting problem. What exactly do you see when you boot the machine?