Hi!

It could be a motor problem with a partially shorted or dirty spindle motor,
or maybe even sticking/dry gears on the sled assembly.

However, from what you describe (the "clicking") it sounds like the unit is
trying to focus on the disc and failing to do so. After a while it will give
up thinking that there is no disc present.

One of the first things to do would be to make sure the lens is clean and
not scratched or anything. The next thing to try is to find a camera that
will show IR light on a TV screen and use that to examine the laser to see
if it is doing anything.

This could be caused by a weak laser, dirty lens, pickup failure, failure of
other parts, or adjustments that have somehow drifted or have been played
around with. The FAQ for this group has lots of information that could help
you fix the problem. Be sure before you ever touch any adjustment that
everything is working to the best of your knowledge. Make careful notes if
you do change things, and good luck!

William