94 GP SE transmission

[K-HOVA]

My Car won't go into gear at all.

This is how it started. I woke up one morning and was off to work but when I started my car a loud sound was coming from under the hood. I was about -17*C outside and I had no time to check on it. So later on that day driving home started having problems with gear slippage. But I had to go out. So I kept driving. The car wouldn't downshift and when it goy up to about 80km it would come out of gear. and wouldn't go into gear till I shut the car off and restarted it. Now it won't go into gear at all. Please Help