thanks to all ok, now i know the bad sector and i have red about it on some web page. they said that there are 2 types of the bad sector : logically and phsically.the first one we can fix it by using some program but the other is difficult. my qutoin now: 1- what cause this problem and how can i save or protecte my disk from it? 2- can this probelm be found on the cd or flopy? 3- how can i know the my hard disk have abad sector? 4- can i get back the data from the bad sector eara?