Unable to import photos from external hard drive to Photos on Mac

Where is the Photos library stored -- internal or external disk? What format is the external drive? Do you use any 3rd party virus apps or "cleaners" that often cause obscure errors and corrupt the system?

laurasdes wrote: … both my Mac and hard drive have enough space. I am very frustrated.

What does that mean? How much free storage? What percent of the storage on your Mac is free?

Do you use iCloud Photos? if so, do you have "Optimize" turned on?

In addition to the things Matti Haveri and Yer_Man suggested, try these steps to narrow things down:

That's weird. To narrow things down, try these steps:

• Restart the computer (of course)
• Re-start in Safe Mode. This bypasses certain potentially disruptive processes, and it often helps. Safe Mode is different for different computers, so see this: 

           Start up your Mac in safe mode - Apple Support 

• As Yer_Man recommended, use another library if you have one, or make a small test Library with a few pictures in it and see if the same thing happens. You can create a new Library by closing Photos and then option-clicking on the Photos icon.
• Make a new user and see if the same problem recurs with it.  This is a bit harder, because a new user can't access a different user's stuff. You would need to move your Library out of your own user's folder up to the general "Users" folder. 
• Rebuild your Photos Library--close Photos and re-launch by option-command-clicking the app icon. If you use iCloud Photos, it’s possible that this will cause a re-sync that lasts long enough to make you nervous.

The idea is to find out if the problem is with the Library, with your account, or with caches and login items, and stuff like that. One of these steps may fix the problem, but their failure to work also helps figure out what's happening.

Let us know what happens…

As a test: create a new library and see if you can import one or two to that.