Q: Taking off parts, cleaning them, replacing certain parts, draining fluid, putting new fluid in. Why won't car move?

I asked a question before, what would cause the car to stop moving? I know it's the transmission. I drained the transmission fluid out, it was dark and smelled burnt. Put 31/2 quarts back in it. Took off 3 solenoids, cleaned all solenoid screens and they tested, good. Replaced the filter and started the car, let it warm up, then put it into reverse, had my foot on the accelerator pedal, gave it a little gas and the car moved backwards. Put it into drive, gave it a little gas and the car moved forward. Turned the car off and let it sit. Came back to car about a couple of hours later, started it up and let it warm up again. But this time when I put it in reverse, it did not move and the same when I put it into drive, it did not move. So, why did the car not move backwards or forwards the second time? I need answers, please give me something like, what else can be wrong with the transmission?

My car has 207000 miles.
My car has an automatic transmission.