Based on your error it seems the system sees the CDROM drive. The boot disk creates a virtual or temporary partition called a RAM drive. It takes the normal place where the CDROM would be. So for however many drives or partitions are in the PC just consider that when using the boot disk the CDROM will be up one more drive letter than normal. I don't think this is your issue because if you thought you had acessed the CDROM but were actually opening the virtual drive you would not have gotten theerror.
Start with the basics, first try another CD disk. The disk being used may have problems. Get a music CD and plug speakers or headphones into the connector in the front of the CDROM drive. If it plays then you'll know the drive is working. Also clean the disk. Does opening and closing the CD tray work correctly and not take a long time?
Usually the CD drivers included on the boot disk works for most but you may need to install the DOS drivers that came with the CDROM drive.
Check the installation of the CDROM drive. Tottaly disconnect it and start over. You may have overlooked something.
Make sure the ribbon cable is correct. The strip on the cable is for pin one. On the drive connector pin one is located next to the white power connector. That goes for all hard drives and CDROMs.
Don't use screws that are too long, and make sure the drive is securely installed. Vibration can cause problems.
The jumper setting for the CDROM is master, slave or cable select. If the drive is connected to the hard drive and those are the only 2 IDE devices installed in the system put the CDROM on a ribbon cable by itself. Set the jumper to master.
Change settings in the BIOS to AUTO detect for everything concerningthe IDE channels.
Ultimately you may need to get another CDROM drive to try out.