Inconsistent CD-ROM

One of my systems is a legacy 1994 Compaq with un upgraded 486 133 CPU – the CD-ROM is now intermittent – that is, it is only sometimes recognized as a drive. However, if you put a music CD in, and hook the headphones to the CD, it always plays. Anyadvice why this might be not recognized about 75% of the time. About every 3 or 4 reboots, the CD-ROM is recognized as the D drive again.