Gears won't change. Can anybody provide some useful advice. ?

Automatics have a gear shift safety solenoid that locks the gearshift/transmission in park unless the brake pedal is depressed. This is to prevent people from dropping into a gear from park and rolling into traffic or backing up over someone unexpectedly. When you press the brake pedal you should be able to hear a clicking sound coming from under the gear shift lever. If you dont hear the sound then the solenoid may need to be replaced. The other possibility is needing to replace the brake pedal position switch (usually attached to the pedal assembly or behind the brake pedal assembly) which tells the shifter solenoid to activate when the pedal is depressed.

I'm not completely sure what your saying so I'll say this. If you can't shift the car into gear with the shifter lever, then it probably has a broken shift cable or linkage. If you mean when the car is shifted into "drive" it won't shift from 1'st to 2'nd to 3'rd, then it probably has a bad shift solenoid in the transmission, or the transmission itself has gone bad. If this does not help, please post again with a more detailed description. I hope this is helpful:)