when i was using CD,at the same time my CD rom drive gets hidden,many a time it happen so in about 5,8 minutes etc...then i go to my computer properties>device manager and scan my computer,CD rom drive comes again,what is the cause of this,reply me thanks a lot

Loose cable? Bad drive? Life's more painless for the brainless.

It is common to un-intentionally damage IDE data cables, especially while removing them - the 80 wire ones are more fragile. What usually happens is the cable is ripped at either edge and the wires there are either damaged or severed, often right at a connector or under it's cable clamp there, where it's hard to see - if a wire is severed but it's ends are touching, the connection is intermittant. Another common thing is for the data cable to be separated from the connector contacts a bit after you have removed a cable - there should be no gap between the data cable and the connector - if there is press the cable against the connector to eliminate the gap. 80 wire data cables are also easily damaged at either edge if the cable is sharply creased at a fold in the cable. Try another data cable if in doubt. That could certainly cause this problem, and data errors on your hard drive as in your other post.