/dev/hda is not a valid block device

[Pollywog]

Yesterday, I attempted to mount the CDROM and I got: /dev/hda is not a 
valid block device.
I have not changed /etc/fstab or my kernel config options, and I had no 
problems until yesterday.
I am not sure just how long the drive has been unmountable, though.  I was 
using kernel 2.4.12 and last night I upgraded to 2.4.13 but the problem 
still exists.

Anyone have ideas on where I should look?
thanks