Crop won't work

[Ofnuts]

The Tool options dialog is a very important dialog and is visible in the default UI:

   

However in recent Gimp version it tends to fly off by itself, and people close that pesky window... and lose it.

To restore it and lock it in place, see this tutorial: Getting the Tool options back, once for all

Also, to manage your UI, see this other one: Managing tool options and window positions