Well, it's not a good idea to turn a computer off while its operating system is updating. It generally loses its sanity, can no longer find the bootstrap software, and hence cannot startup normally afterwards. That's why this has happened to your device, and it's why Windows Update (for instance) warns you not to turn off your computer until the update is complete. Same thing here - it's a computer.
You may be able to get it back to a sane state by starting it up in safe mode. To do that, hold the DOWN nav pad key while powering up. If it gives you a stable display, run Line 6 Monkey and reinstall the firmware. Do not disconnect the USB cable during the update procedure.
After the update, power up while holding down the Left nav key to r eset the Global Parameters.