I was driving down the road at about 20-25 miles per hour, and my toyota corolla decided it wanted to stop.. and boy did it stop. If I didn't have my seatbelt on, i would have been thrown out the windshield. I would stop on a dime. I started it back up, put it in drive (automatic transmission) and about a block down the road it did it again! I managed to limp home, about 1 mile, that way. It starts just fine, but when I put it in gear, it grinds horifically, and then shuts down. What could this be?