Can't access CD ROM, explorer keeps hanging ??

Used to have a single CD ROM, set up as master at the end of the cable.
Added another CD ROM, for R/W, set up as slave.

Boot up everything lists ok. Yet, can't access information on CD ROM

Went back to single CD ROM [original setup] and still disk won't read
info. Worse, Windows Explorer badly hangs trying to read the disk.

google searches yielded a lot of "perfect" informative resources which
are gone! ...as usual.

A check with the manufacturer who now only makes PC MotherBds : "aw,
it's just standard. Try changing the jumpers all over." Wouldn't
changing back to the original setup cover that?

Can't install any Windows 98 from my CD now and the "auto play" feature
doesn't even automatically play a music CD like it used to.

Where to look, what to do?

- Robert -