Try a battery pull.
If that doesn't work, try a Hard Reset.
1. Power off phone
2. Use hardware keyboard
3. Press and hold the 'X' key and Power button until you see a screen with an exclamation point inside a triangle
4. Press and hold the Volume Up key then press the Camera button (I had to do this twice) to get menu screen (Linux back-end becomes VERY apparent here)
5. Using the D-pad, select one of the Wipe options (specifically Wipe Data/Factory Reset)
6. Confirm your selection and wait for it to complete
7. Reboot the device