If the Disclaimer shown at startup is not accepted, the application may hang, meaning that it cannot be closed correctly. As a result, PLAXIS 3D cannot be started again.
When this happens, terminate the Plaxis3DInput.exe process using the Windows Task Manager (press Ctrl+Alt+Del, then select the "Start Task Manager" option). After this, you can restart the PLAXIS 3D Input application, and you may accept the Disclaimer to start using the program.
This is fixed since PLAXIS 3D 2011.01