1993 Ford Explorer will not go into gear

My explorer will not go into gear, I turned off my 4x4 last night and when I didi it made a buzzing noise! I tried to turn my 4x4 on again but it just made the same buzzing noise in the rear. I then tried to put it in drive and it would not move, I then tried to put it in any gear and it still would not work. I then put it in park and there was a grinding noise like you would hear in a manual tranny that had missed the clutch. And slowly stopped grinding. I checke the tranny fluid and it was fine. I had it towed home and when the driver took it off the lift it started to roll away while in park.

I can't seem to figure out what is going on I don't know if it the shift solenoid, the kickdown cable, or the torque converter. I have talked to 3 mechanics already the first said that the gear or chain was goin in my tansfer case, the other 2 think that the transmission is between gears