I'd be guessing that it is opening but somewhere off the screen.
Can you increase your screen resolution and see if you can see it then?
You could try a different Work Environment (one of the standard Archicad ones).
That should reset the palettes to there default location.
Problem is when you switch back to your own custom Work Environment you palette will be lost again.
You could also Export the Work Environment from one of the other machines and Import it to the one that is not working.
You can Export/Import the entire Work Environment or just the Palettes section if you want.
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