Warning ! is all I can get.

What kind of photos are you having in your Photos Library? Are the photos JPEGs or in another format?

What does the Info show? The exclamation point could also mean, that the format of the photos is not supported by your system version.

• Incompatible files could be HEIC images then with on a iPhone or iPad - the system version shown below your original post ( OS X 10.11) does not support the HEIF format used by newer iOS versions - you would have to upgrade the Mac to macOS 10.13.
• Incompatible files could also be RAW files in a format not supported by the system. Your system version supports these camera models: Digital camera RAW formats supported by OS X El Capitan - Apple Support

Which camera have you been using and which format are the images? Look at the Info for a photo you cannot export. You can open the info with the keyboard shortcut ⌘i. Can you export the photos with "File > Export > Export unmodified Original"?

Where is your Photos Library stored? Are you keeping it on an external volume or in your Pictures folder?

What has happened, right before you could no longer access your photos?

Did you perhaps run a cleaning application to remove duplicates?

The most likely reason you are seeing the exclamation mark is because the underlying photo file is missing or the library has become corrupted and lost the link to the photo contained in the photo library package.

When you say you are trying to ‘get photos from Photo’ do you mean export the photo? Are you able to zoom in on the photo or edit it?

Do you maintain copies of your photos outside of Photos?