MyPC not detect hard disk . but it detect CD /DVD Rom .
so why this problem arise give me the solution.
i have interchange the data cable also in motherboard .
pl. give the solution

Maybe your hard disk is crashed. So try another hard disk if it detect by mother board that means your hard disk is gone crashed. if not there must be problem with your mother board.

a disconnect every thing else cdroms and other hardrive's
b would be to swap the ide cable to a different one
c would be to swap the power cable to a different one
d if the hardive is set on cable select set it to master / or slave

and if that doesnt do anything it might be done for and you might have to declare it dead

You might try putting the hdd and cd drive on the same cable (assuming that they are both IDE) putting the hdd as master and cd drive as slave or vice-versa. Usually when a hdd is dead you can hear a rhythmic clicking sound coming from the drive. (sounds a bit like a car's turn signal but quieter)

disconnect all drives except the hard drive and try booting up