problems in mounting cdrom

[Patrizia Canton <cantonpa@unive.it>]

Hi,
I am new to Debian and to Linux,
after installing it, I mounted many times the cdrom
with no problems. Today I tried to install apt
and, when I was requested to select the install source for apt,
I was not able to continue
either giving /dev/cdrom or giving /cdrom.
After that when I tried to mount 
mount /dev/cdrom /cdrom     
(which is the entry I have in /etc/fstab and
that it worked till this morning)
the prompt is always 
mount: /dev/cdrom is not a block device.
What should I do?

Patrizia
cantonpa@unive.it