To use mount /cdrom, a proper entry must be in fstab. If it's not there, or points to the wrong device, it won't work.
Try something like:
mount -t iso9660 /dev/hdb /cdrom
(where hdb is the 2nd channel of the first ide slot, change if necessary)
If that works, then you can permenently add it to dfstab and even set it to auto mount.
Edit: Some corrections.
And "mkdir /cdrom" if this path doesn't exist!
