Photo in "Photos" won't open on MacBook Air. Get an exclamation point instead!

filmcell wrote:

Photo in "Photos" won't open on MacBook Air. Get an exclamation point instead! ...

An exclamation point could mean an incompatible file format or a missing original.

A bit more information might help.

• What is the file format? Are the photos JPEGs, or HEIC files, or RAW files? If RAW files, what is the camera model?
• Which system version is installed on your Mac? That will determine, which file formats should be supported?
• And what has happened, before this problem first occurred? Did you upgrade to a new system version? Import new photos? Move the library to a new location? Did you run any cleaning application to remove duplicates?
• Are you importing the files by copying them into the library or is the "Photos > Preferences > General > Importing: copy items into the Library" disabled and you are referencing the Photos outside the library?
• Has the Photos Library been syncing with iCloud Photos?

First thing to do is try to revert edits to original

Select the image, then in the image menu select "revert to original"