To enter service mode do the following:
1) Press the mute button on the RC once.
2) Press the mute button again, and hold it down.
3) With the mute button still held, press the Menu button on the TV.
But to be honest, there's no way the adjustments (which are stored in EEPROM) are going to be affected by a 'knock'.
More likely the tube has been damaged, or the PCB cracked.