My friend's Nuvi 3790 T SG/MY also got the same problem. He had upgrade the FW from 2.30 to 2.50 SG/MY and copy the Thai Keyboard into the device and it stop at " Loading Maps". I think he might got the wrong version of Keyboard.
Now the problem is that the computer could detect the device by USB. Does anyone got the cure or service firmware for Nuvi 3790T SG/MY in order to access to USB and delete the file.

Please help. Thank you.