Transmission completely blinding out?

Okay. So, I bought this vehicle listed above probably about 4 months ago. It seemed like it was going to be a pretty good car, it seemed like I had a pretty strong engine, and it hadn't been doing any kind of warning signs or red flags. As far as the transmission goes, it wasn't slipping or shifting hard, it was driving perfectly fine and normal and didn't give me any problems. I got on the highway the day before less I get on the highway and it completely loses all acceleration all together, will not go in any gear at all whatsoever, won't accelerate at all whatsoever no matter how high rev it, and even after putting it in park it wanted to roll backwards, I had to put the e-brake on to keep it from rolling. I'm very disappointed I thought this car was going to be a decent little car and I've put all my money into it. It's just weird how it went from perfectly fine no warning signs not slipping or shifting hard to absolutely out completely. Is there anything else that I should check? I almost forgot to mention I have check the transmission fluid level. It's normal and the fluid looks like it's in good condition not burnt no debris in it or anything. It will not go into any gear or move at all and then there were a couple times when putting it revenant high or putting it back into Park after trying to get it to go into a gear I heard a grinding sound or crunching some.