Q: Photos won't open

- it says there is an unexpected error and I need to quit

This error message is usually in a panel with a "report" button.  If you click "report", you should see a more detailed error report.

Could you copy and paste the first fifty lines into your next answer, so we can see the exact error message?

Where is your iPhoto Library stored?  In the Pictures folder or on an external drive?

Does Photos launch, when you hold down the alt/options key while launching Photos by clicking the icon in the Dock?

• If yes, then select to create a new Photos library from the panel that will appear and import a few photos for testing.
• If not, then Photos does not work at all in your user account, and then try, if Photos can be launched, if you sign out of your regular user account and sign into the guest account. If even the Guest account des not work, you are having a system wide problem.

If Photos does work on a new library,  repair and rebuild the original iPhoto Library and try again to open it in Photos.

• Make a backup copy of the iPhoto Library, if your backup  is not current.
• Hold down the key combination alt/options key and command key ⌥⌘ while double clicking the iPhoto icon. Select "Repair database" and repair the library. Repeat with "repair Permissions".
• If you still cannot open the library in Photos repeat with "Rebuild Library".

My photos - and there are many - are stored on the hard drive

Does that mean your iPhoto Library is in your Pictures folder in your Home folder or in a Shared folder?

  I still have my iPhoto library which is near complete.  But even that is playing up and won't show the most recent events even though the last import is visible.

That is usually caused by sorting the events incorrectly.

Select the "Events" in iPhoto and try to change the sorting of events to "View > Sort Events > By Date  Descending"

Since you are seeing the last import in the Last Import album, you can also try to find the corresponding event by selecting one photo in the Last Import album and ctrl-clicking it.  Select "Show Event".

The pictures I tried to export to Photos before it crashed were from a file transfer website called wetransfer.com.  I wonder if that could have caused a major meltdown?

Did you download the photos to a folder on your Desktop and import from there?  What is the file format of these files? Are the files JPEG or another format?

I'm not able to open Photos, either.   I tried getting an old library from the time machine, copying that and opening with that and it won't work.  Here is my error message:

Process:               Photos [898]

Path:                  /Applications/Photos.app/Contents/MacOS/Photos

Identifier:            com.apple.Photos

Version:               1.0.1 (215.65.0)

Build Info:            PhotoApp-215065000000000~1

Code Type:             X86-64 (Native)

Parent Process:        ??? [1]

Responsible:           Photos [898]

User ID:               501

Date/Time:             2015-09-01 14:20:35.613 -0400

OS Version:            Mac OS X 10.10.4 (14E46)

Report Version:        11

Anonymous UUID:        E6B377BF-57B3-7866-836F-33854483F9F1

Sleep/Wake UUID:       2D50BDF9-4877-49D3-9CB7-28C809219D25

Time Awake Since Boot: 6300 seconds

Time Since Wake:       870 seconds

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_BAD_INSTRUCTION (SIGILL)

Exception Codes:       0x0000000000000001, 0x0000000000000000

Application Specific Information:

Photo Foundation logging:

2015-09-01 14:20:00.861: Received changes notification alert: <LiModelChangeGroup: 0x60800106fc00>  alert flags : Replay Complete (__59-[RKFaceChangesHandler startListeningForChangesFromMarker:]_block_invoke_2:173)

Crashing on exception: *** -[NSConcreteTextStorage attributesAtIndex:longestEffectiveRange:inRange:]: Range or index out of bounds

Does this make any sense to you?  Can you help? Thanks so much!

I don't know if you fixed this, but I had the same issue and discovered I had no Photos folder in my Pictures directory. I created New and named it Photos Library. That fixed it.

This is exactly what was happening to me. Kept trying to load Photos but it never got past 0% loading, with no other options to select. I always got the same error message as you are seeing.

What fixed it was that my Photos Library document was not in a "Photos Library" folder. So I created a new folder, named it "Photos Library" and moved the Photos Library document to that folder. Now when I open Photos I was able to select the iPhoto document to upload and have that begin uploading to Photos.

Go figure why that made a difference...

This worked for me too.  Thanks!

I have the same problem, but nothing from the suggestions above seem to work.

Ok - then you need to start a new thread with the specific details of your system and your problem so someone can assist you - this thread is very convoluted and is about several different  issues, answers and software versions - you are move likely to get good assistance if you start a new thread for just you  --  see Writing an effective Apple Support Communities question for assistance in writing an answerable question

LN