It would be nice to see what your "fdisk -l" output shows. Otherwise I'm just guessing here. I don't know what /dev/sdb5 is. I'm assuming that's your LVM physical volume. You don't mount this directly if this is indeed the case. You mount the logical volumes contained within /dev/sdb5 (which is a physical volume, part of a volume group, which contains logical volumes - or so I'm assuming).
It sounds like you removed the disk from it's original machine and now have it installed on a second machine. Correct? That second machine will need to have the LVM software installed, if it doesn't already. Now, on that second machine, run "vgscan" and then "vgchange -a y". Then run "ls /dev/mapper" and see what shows up. Hopefully your logical volumes will. You should then be able to mount them. Something like the example below:
# vgchange -a y
# ls /dev/mapper
( this should should list things like /dev/mapper/XXX-YYY )
# mkdir /mnt/tmp
# mount /dev/XXX/YYY /mnt/tmp
# ls /mnt/tmp
From your description, it sounds like you're probably only missing the "vgchange -a y" part. The rest I included only for completeness.