Transmission system hard to shift gears

I started experiencing unusual sound from the engine like there is difficulty in switching to next speed of gear (low and high engine sound when driving). And when I shift gear selection to reverse mode, I get humming and slight grinding sound from engine and eventually, the gear started disengaging on motion. I had some speed sensor replaced and the transmission oil changed, but finally the transmission system. I can no longer drive the car and the gear selector light does not flash. What can you advice please?

Can a self reset work, and how do I do that?