Having read about it elsewhere, I took the opportunity to remove the Pentium 200 MMX CPU and replace it with a K6-2 400 CPU.
As part of doing this, I (a) flashed the BIOS with a newer patched version which allowed the motherboard to work properly with the K6 (see http://www.exit109.com/~scotth/1571/ ), and (b) then reset the CMOS as directed by the flash procedure.
(I have a 3.25G hard drive as C: with Windows 98SE, as IDE primary master, and a 6G hard drive as D: as secondary master; both are Maxtor drives. I have a 4/8G tape drive -- Seagate STT8000A -- as primary slave, and an older Compaq CR-587 CD-ROM as secondary slave.)
Since then, my CD-ROM has been acting strangely. If I insert a game CD (something like a simple Boggle from Hasbro), the autodetect works fine, although a little slower than usual; I can then play or install the game with no problems.
However, most other CD's -- including my Windows 98 SE CD-ROM -- aren't recognised. For example, I've also pooched my LPT driver. I try to reinstall the driver, it asks me to insert the W98SE CD-ROM. I do so, but it reacts exactly as if I hadn't closed the drive, or if I'd closed it with no disc inside. When I try to use DOS to look at the files (dir E: ), it says 'Drive not ready'. (Funnily, with a game CD such as the Boggle one mentioned above, I *can* read the directory from DOS.)
I'm guessing that in resetting the BIOS settings (by erasing the CMOS), I've set something wrong so that the system can't see the CD-ROM properly. I've tried changing 'PnP OS Installed?', 'Resources Controlled By', 'PCI IDE IRQ Map To:', but no luck.
Any ideas?

Thanks!!
Robert