CD-ROM starts spinning and then stops repeatedly even if I do not insert any CD in it and computer hangs for a while during this process. Why is so ?

I would hazard a guess that something in your system is checking the CD/ROM for some file. The problem is going to be finding out what.

Check your Startup (use MSCONFIG) and see if there is anything there that might be the culprit.

Well... I've formatted the drive thrice, tried different OS (XP, 2000, 98) but the same problem appears... nothing in startup... but still the problem is there...

Can you try the cd rom drive in another machine? Sounds like it's time for a new one!

Hello,
I've had the same problem serveral times on different machines, I've replaced the CD-r with another good one, and the problem disappeard.
Inserted the same CD-r ( the one which was causing the problem ) in another computer and got the same problem, so that will say simply that the CD-r is faulty.

Greetings