One concern I have is that maybe the external drive isn't properly formatted for Mac. This happens a lot-- most come from the vendor formatted in ExFat or something like that, and the new Photos app can't work with that. So if that's the case, you may have to re-format the drive in APFS format or Mac OS Extended (Journaled) format, and re-copy the iPhoto Library to there. See this:
Move your Photos library to save space on your Mac - Apple Support
The newest Photos apps won't run an iPhoto Library, but kaz-k suggests, you can open Photos and choose File>Import and pick the iPhoto Library to load in all the pictures into Photos. Unfortunately, you don't get iPhoto Events -- just a mass of pictures.
If you would like to preserve the structure and organization of the iPhoto Library, the best thing to do is to use the trusted 3rd party app PowerPhotos ($30.) This is especially good at handling multiple Libraries, including those from iPhoto.
Can you see the pictures on the 2010 MacBook Pro? Does iPhoto work for you there? If so, you can export pictures to your (properly formatted) hard drive like this:
EXPORTING A PHOTO:
1) Click on File, then click on Export.
2) Click on the Up-Down Arrow button next to Kind:, then select Original, Current, JPEG, TIFF or PNG. (JPEG is probably the best choice here, because it is a compressed format that is widely used on the Internet and in e-mail.)
3) Click on the Up-Down Arrow button next to Size:, then click on Small, Medium, Large or Full Size. (Select Small or Medium if you are going to be e-mailing this picture; click on Full Size if you want the highest possible resolution in the image.)
4) Click on the Export button.
5) Type a file name in the Save As: box, such as Hawaii vacation 2008.
6) Click on the Up-Down Arrow button next to Where:, then select the Desktop or whichever folder you want for the destination for this picture file.
7) Click on the OK button.
(I copied this from iPHOTO INSTRUCTIONS that I found with Google.) If you have questions, ask us. There are some people here who have much more recent experience with iPhoto than I have.
