Check the cables inside the computer that connect to the CD drive...both the power
and data cables.  I would try replacing the data cable, and if that does not help,
the drive may be defective.  But before jumping to that conclusion, I would try
booting with the emergency boot floppy disk with CD-ROM support, and at the A:
prompt, see if you can read a disc in the CD drive from DOS.

To do so, put the Emergency Boot Disk in the floppy drive and restart the computer.
It should boot from the floppy....if it does not, you will have to enter the BIOS
Setup program and set the boot sequence to Floppy first, then hard drive.  When the
floppy boot begins, use the arrow keys to select "With CD-ROM Support" and press
Enter.  Watch the screen, as the CD drive letter will be on-screen just prior to the
final A:\ prompt.  At the A: prompt, type the letter of the CD drive given to it as
seen during boot, followed by a colon (:), then press Enter.  That will put you at
the CD drive.  With a disc in the CD drive, type DIR at the A: prompt, and press
Enter.  Does a file list flash by?