Problem with my external CD-Rom

[Dellacherie Stephane]

Hello,

If my external usb cd-rom is connected when I boot my laptop, there is 
no problem to mount and do umount my cd-rom.

But, if I boot my laptop and if, *after*, I connect  my usb external 
cd-rom, it is impossible to mount the cd-rom.

What happends ? Is there something to change in the files /etc/fstab or 
/etc/mtab ?

Thank you for your help !

Stéph

postscriptum :

My /etc/fstab is the following :
======================

LABEL=/                 /                       ext3    defaults        1 1
LABEL=/boot             /boot                   ext3    defaults        1 2
none                    /dev/pts                devpts  gid=5,mode=620  0 0
none                    /dev/shm                tmpfs   defaults        0 0
none                    /proc                   proc    defaults        0 0
none                    /sys                    sysfs   defaults        0 0
/dev/hda5               swap                    swap    defaults        0 0
/dev/sda1       /mnt/cle_usb vfat defaults,noauto,user 0 0


My /etc/mtab is the following :
======================

/dev/hda3 / ext3 rw 0 0
none /proc proc rw 0 0
none /sys sysfs rw 0 0
none /dev/pts devpts rw,gid=5,mode=620 0 0
usbdevfs /proc/bus/usb usbdevfs rw 0 0
/dev/hda2 /boot ext3 rw 0 0
none /dev/shm tmpfs rw 0 0
sunrpc /var/lib/nfs/rpc_pipefs rpc_pipefs rw 0 0