dont panic, sounds like the ide cable may be slightly adrift, as a first check both ends are pluged in ok. next possibilty is the bios has not recognised the drive correctly, try going into bios and use auto detect ide drives. and make sure that the master slave jumpers are correctly set. so far no damage should have occured to the drive or data.
if the above checks out and there is no change, i'm sure there be others with more ideas.
Rickity