External hard drive not showing a drive letter

I have an external hard drive enclosure that I normally use with an a 250GB SATA HDD for backups. It works fine. But I also have another SATA HDD (a 500GB one) that I recently took out of my laptop that I replaced with an SSD. The HDD still was good, and has an active OS on it. I could put it back in the laptop again and continue where I left off if needed. But I recently put it in the enclosure to use its empty space (which is about 400GB), but it doesn't show a drive letter in Files Explorer when I plug it into a USB port. I connected and disconnected several times, but no drive letter showed up. It always made the 2-tone sound that indicates when I plug in and unplug, but that's it. Then I put the 250GB drive back in the enclosure and tried again, and then it worked. So it's a HDD problem and not a problem with the enclosure.

Would I have to erase what's on the 500GB drive in order to use its empty space, or to do anything else with it as an external drive?

Run diskpart and type in automount to check where automatic volume mounting is enabled.

spunk said:

As stated, press the Windows key+X choose Disk Management. Here, in the Lower Pane right click your drive and choose Change Drive Letter or Paths. Choose a letter not being used.

I wasn't able to choose a drive letter at first. But I noticed that it showed the disk as being "offline". When I right-clicked the drive, a pop-up menu included the word "online". There was also a notice that briefly appeared as I hovered my pointer over it that said something about it being offline because it conflicted with the other disk (my internal drive). I didn't get to read the whole thing because it disappeared too fast. Now, the disk is showing as online, with a drive letter of OS(E), which is similar to my internal drive which is OS(C). I could see how there would be a conflict. I see where I can right-click to change the letter. However, since it's currently being read as an OS drive, would that cause any problems for my computer? After all, it is a hard drive with an active OS on it.
I'm including a screenshot so you can see what the Disk Manager screen looks like. Disk 1 is the external HDD in question, and Disk 0 is my internal SSD.

When troubleshooting drive recognition view:

a) BIOS
b) disk management
c) device manager


These software may be useful:

View / Change / Remove drive letters assignment in your system

View any installed/connected USB device on your system

spunk said:

What do you plan to do with this External Drive with Windows on it? You cannot boot Windows from an External Drive. Do you want to use the drive for Storage?
To avoid confusion, I would first right click the E: drive and rename it something other then OS, like Backup or Storage whatever. Maybe also choose a drive letter lower in the alphabet.
If you want to prepare the drive to use as storage, and there are files on it you wish to keep, I would save them to another drive temporarily, then I would Delete All of the Partitions on Disk 1 that includes the E: drive, leaving it all Unallocated Space. Then right click the space and choose to make a new Simple Volume, taking up the space, and Formatting NTFS. Then you can restore the files that were previously on the drive using it now for storage. Or leave it the way it is.

I was planning to leave it as it is. It's the HDD I was originally using in my laptop, which is why it has an active OS in it. Only 96GB is used, and 356GB is free, so I would like to use it for external storage, but also be able to simply put it back into the laptop if my replacement SSD turns out to be faulty someday. One never knows!
If I change the drive designation from OS(E) to something else, would that affect it's ability of it's active OS to work the way it did before if I re-installed it as an internal HDD? I assume it would, but of course not sure. My guess is that an OS designation would be assigned to it once it was re-installed and was booted from.

Back up images allow end users to recover after:

corruption of the operating system
corruption of the registry
corruption of the component store
corruption of the drive file system
ransomware
malware
failure to boot
drive failure

etc.


Macrium Software | Reflect Free Edition
Backup and Restore with Macrium Reflect


Others:

Acronis, Aoemi, EaseUS, Paragon, etc.

zbook said:

Back up images allow end users to recover after:

corruption of the operating system
corruption of the registry
corruption of the component store
corruption of the drive file system
ransomware
malware
failure to boot
drive failure

etc.


Macrium Software | Reflect Free Edition
Backup and Restore with Macrium Reflect


Others:

Acronis, Aoemi, EaseUS, Paragon, etc.

Yep, and I do have Macrium Reflect which I used to create a backup image onto a different external HDD, and then to restore that onto my new SSD that I'm currently using.