I have a 96 v6 mustang with only reverse no forward gears out of the blueU

What is your question?

I have a 96 v6 mustang with only reverse no forward gears unless I rev the motor up to 4000 rpms I feel like it is something real simple and noticed shortly before the tranny going out the brake warning indicator light was lit up and stayed on. Could the brake warning indicator light staying on be a reason there is no forward gears, maybe like some sort of safety feature?