Running Ubuntu Debian, 4.10. When boot process gets to "Loading Modules" it slows to a crawl and can take up to 20 minutes to finish booting, but it does always boot. When it gets to "Enterprise Volume Management System" it gives this message - "hdc: drive not ready for command"
Here is a block of data from dmesg:

ide-cd: cmd 0x1e timed out
hdc: lost interrupt
hdc: lost interrupt
hdc: lost interrupt
hdc: lost interrupt
hdc: status error: status=0x59 { DriveReady SeekComplete DataRequest Error }hdc: status error: error=0x50LastFailedSense 0x05
hdc: drive not ready for command

I've been told that I've got a bad CDROM. Does this make sense?

from what you've posted, hdc should be the cdrom. It sounds like its unable to communicate... I'd attempt to replace the cdrom.

Replacing the cdrom resulted in no boot at all. It stopped at 'hdc not ready for command' whereas before replacing, I got same message but it eventually booted, usually after about 15 minutes. After replacing, I left the computer on all night and by morning it still hadn't booted.

What does the computer do without the CDROM installed at all? Is this an onboard controller? Can you change IDE cables?

Last but not least, do you get error messages with the new cd, even though it doesn't boot?