System not detecting hard disk

Question

i have 20GB samsung hard disk.i used to transfer large data through inserting my hard disk into friend's PC.once when i inserted it his PC was not able to detect both hard disks i.e.his & mine both hard disks.when i removed my hard disk ,his pc was detecting his hard disk as before and was working fine .so i dont know wht happened to my hard disk and is it now reparable or not.wht shud i do??please tell me.