You need to check and see if the data is still on the drive.
"No bootable device" could be something simple like the partition not marked active anymore.
Or it could be something serious, the drive could be dead.
Unplug the external drive and boot the reovery disk again and use the option to open a comand prompt.
(I can't remember where that option is, I have not used the tool in a long time).
Type: C:
then press enter
(that should change you to the C drive)
then type: dir
then press enter
that should give you a directory list and you should "see" if everything is still on the drive and accessable.
If you have problems trying to do that with the NBRT you may want to try another bootable disk like partition wizzard or a Linux disk like puppy or ubuntu.
If the data is there it should be very simple to fix the system so it boots.
If the drive is not working or it shows a corrupted partition then the drive may be dead.
Best of luck
Dave