What does it say when you try to boot to XP? When did you install XP in the whole process of things? Was it the first OS or the middle OS or the last OS? We cant tell you what the cause is with such little information. That would be like trying to diagnose a persons cold when told they have a tickle in their throat. It isnt possible to answer this type of question.
For Win7 to say you have a hard disk error means exactly that. You need to run chkdsk /r /f on the drive. It has bad sectors and is possibly close to failing.
