Check the A/T fluid. If it is ok, seek professional help. Continuing to drive it can do some serious damage.
my car is not working in 1st gear
change the transmission not the motor
When the shifting linkage is disconnected the car will appear to go into gear but not move. The car will not move when the transmission fluid is low.
When shifting a manual (or standard) transmission on a vehicle, if you hear excessive knocking noises immediately after shifting, you are probably:1) Shifting into the next highest gear too soon, or2) Shifting into the wrong gear - for example, going from 2nd to 4th gear, or3) Not running the engine fast enough after shifting to the next highest gear, or4) Your engine is out of tune if you know you're doing steps 1,2 and 3 correctly
The car is attempting to find the next gear, stopping the car while finding it, and then moving on.
The car isn't necessarily shifting into neutral its just staying in a lower gear and not shifting to the next gear, check your transmission fluid.
rpm too low maybe you are shifting to soon
If it's an automatic, your transmission may be dying; if you drive a manual, you're probably letting the clutch out too fast.
its not if you have overdrive its shifting into it it feels like its down shifting but it really isnt.
If a transmission for a car becomes stuck between 1st and 2nd gear the fluid should be changed. Old fluid in a transmission can cause hard shifting and stuck gears.
Gear shifting has little to do with batteries, or your car's electrical system. If your car is stuck in one gear, your clutch (on a manual) or even worse, your transmission, might be going out. The dead battery might be just a coincidence.