if you are trying to attach mass storage device(USB) or DVD Drive or Windows Partition then it won't automount it and instead will return an error citing "cannot lock media/.hal-mtab" .while try to access the device.here is quick fix-

make a directory mkdir /mnt/sdb1 #sdb1 is for Pen drive,change it with the desired partition like /hda or /sda1,/sda2 etc.

mkdir /mnt/sr0 #for mounting DVD/CD Drive

add the USB device/HDD Partition/DVD/CD entries to /etc/fstab
for example if its sdb1 it should look like
nano /etc/fstab
/dev/sdb1 /mnt/sdb1 vfat auto,noatime,users,suid,dev,exec 0 0 #Autoupdate
change vfat & /dev/sdb1 with the format e.g ntfs-3g etc & corresponding file system.

Read my tutorial on Dual Boot BT4 with Windows and there I have mentioned how to mount different partitions including NTFS-3g,vfat etc.