When i format my pc with win xp before enter the register key a problem show wit

A blue screen? It could be lots of things.
Does it points to some *.dll file or to a *.sys file?
Try borrowing another xp cd and try with that
Try restoring bios to default
Try a chkdsk from recovery console
-boot fom cd, press r, press 1 (usually) , type password and press enter, or just press enter if U don't have password.
Type
chkdsk c: /r and press enter
Does it complet the format or not?
If U get this when U try to format, U can try to format by recovery console
Type
format /? to see commands
(usually format c: /q FS:NTFS )
Be carefull ! c , if this is the partition U need to format
q mean quick
FS the file system type