How can we use bartpe /PE or XP live edition to repair our system if we can' t access the hard drive? How can i copy the file from the damaged HDD to another HDD through bartpe?

wild guess:
SATA, SCSI or just another controller not supported by XP out of the box.
In that case you will have to add the matching drivers to BartPE. I think it was in the docs into which folder you have to put the driver files.