Cannot assign a drive letter

Hi folk.
I have an external drive where the electronics of the case has failed. I have switched the drive into my pc so that I can use it as an internal drive. The drive is still operational but I cannot see it listed in my drives. Opening up disk manager shows the drive is clearly visible there but is no volume letters assigned to it.
The easy option would be to delete the partitions and create new. However, the drive is divided into several partitions which I want to keep as they contain a lot of important data files (years of photos for one thing). Disk manager wont allow me to assign any drive letters (option is grayed out) and disk partition only shows me a single partition not the 5 partitions I have on the drive.
so my question is how do I assign volume letters without losing my data?

It sounds like your partition table has been lost or corrupted. Please post a picture of disk management screen to be sure Screenshots and Files - Upload and Post in Ten Forums - Windows 10 Forums

If it has you should be able to recover your partitions with MiniTool Partition Free or similar software as long as you don't write anything to the disk before hand.

Ok here is the disk manager screenshot

Look's like halasz is right. You will need a new disk to copy the recovered data. Once done, wipe all partitions and create them again. If the disk has no physical damage (only logical) you should be OK. Since the recovery tool will search sector-by-sector it can take hours before letting you see and copy any data. Be patient, I have been through similar situations and I know how it feels.