My 2004 Honda Accord just starting locking itself automatically. It never did this before and I don't like it. How can I go back?

Take car to dealer lock system needs to be reset. Some vehicles lock when get to a certain speed your vehicle simple needs a reset.

does the dome light come on when the drivers door is opened, if not the pin switch is bad

driver side has most use and breaks down quickest.
Typically, the lock wears, and should be oiled using graphite powder, not oil, as with most outdoor locks.
However, in winter moisture turns to ice and freezes lock.
In this case, try to squirt lock de-icer (usually this is methyl alcohol or some other type).
Don't use an alcohol (such as from drugstore) that also contains water.
that would make matters worse.
If you spray enough lock deicer or even a high-quality penetrating oil, you may be able to work key and lock to a point where you can turn it.

Don't force key rapidly or too strongly, as it will bend, and may break off in lock.

You can spray some alcohol or penetrating fluid on the key to work it into the lock better.
Sometimes, you can get at a frozen lock mechanism by spraying down into **** between window and metal door from above lock.
Sometimes, you might find that the door itself is frozen,
or the lock latch is frozen, and not the key-tumbler.
In this case, you can try body-checking (not kicking) the door,
to loosen the frozen edges around door and window.
If you can get into car from other side, you can sometimes open it from inside to break ice-jam.

If this is an electrical problem (only remote doesn't work)
The likely cause is broken wire in wire-harness from car body to door.
There will usually be a group of wires either inside a cable or bundled in a rubber tubing, going from car to door at front between hinges.
Here is where the electrical connection will be broken,
because the wires break eventually as they get flexed over and over.

IN this case, the only permanent fix is to find the wire (it will be color-coded), and replace at least 6 inches of that wire (it will probably be broken inside insulating sheath.)
Alternately, there may be an open-circuit at connector to door-latch solonoid. Here you might get lucky if you get inside door-cover off and wiggle or re-insert the plug connector.
Also possible that solenoid is just burnt out or open-circuit.
In that case it must be replaced, for the remote signal to effectively open door lock.

could the cars battery be flat by any chance

this could be broken wires in the space between the body of the car and the door panel itself.other wise it sounds like the door locks in the doors are bad.you don`t say if this started all of a sudden or one door started to not work then another and so on.its possible that it is the wires coming from the switches them self going to the other doors.

You most likely have a fault with a computer. Unless you have wiring daigrams and a low impedance multimeter and the knowledge to not cause additional damage I would take it to the dealer since you may need reprogramming after they fix it.

No. Not at all.

Gently rock the steering wheel back and forth against each place it stops while trying to turn the key. DON"T use any force here! You may consider shooting a spray lube into the key slot also.

DOES SYSTEM INTAKE CODE YOU TYPE AND RETURN WITH ERROR MESSAGE OR JUST PLAIN HAS LOCKED SCREEN? SYSTEM IS DESIGNED SO THAT IF INCORRECT CODE IS INPUT MORE THAN THREE TIMES SYTEM LOCKS ITSELF.WHICH REQUIRES THAN THE NAVI UNIT BE UNPLUGGED FROM BATTERY POWER FOR ABOUT 5-10 MINS TO RESET ITSELF.NOW INCORRECT CODE CAN BE DUE TO WRONG CODE/SERIAL # CARD FOR VEHICLE, UNIT HAS BEEN REPLACED IN PAST POSSIBLY AND YOU ARE INPUTING CODE FROM OLD UNIT UNKNOWINGLY. YOU ALSO WANT TO MAKE SURE CODE YOU ARE TRYING TO INPUT IS FOR NAVI-SYSTEM AND NOT THE RADIO CODE FOR THE STEREO. IF ALL ABOVE CHECKS OK THEN NEXT STEP WOULD BE TO REMOVE UNIT TO RETRIEVE SERIAL NUMBER FROM BACK OF NAVI UNIT THEN GO TO NEAREST DEALARSHIP WHO CAN THAN RUN S/N THROUGH HONDA IN SYSTEM AND RETRIEVE CORRECT CODE FOR THAN SERIAL NUMBER. LET ME KNOW HOW IT GO'S

Do you mean the automatic door lock won't lock or unlock? If so, you need an actuator replacement.