Hi,
Sometimes the CD-ROM drive does not read cds and a drive letter is not shown on a dell optiplex GX 280 machie.
Could you tell y?

Any changes that either happened or that you perhaps made to your computer around the time that the problem started; particularly any software or hardware that you installed or setup.

Go into control panel and the system icon then the hardware tab and device mgr.

Is your cd rom listed there or are there any yellow marks present