Any particular messages when you try to open it?
Does the progress bar get stuck at a certain point or does it not even get that far?
Years ago I experienced a problem where a file wouldn't open and I think it was getting stuck while loading the "header" stage.
I found if I opend a similar file, left this file open and then go to the FILE menu and OPEN the bad file (do not tick launch new instance of Archicad), then the file seems to read some of the old information from the other file and opened.
If this doesn't work you could try MERGING it in to another (similar) file.
Archicad usually makes its own backup file with a BPN extension.
Have you tried opening this?
Barry.
One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11