There are several possibilities.
1. Many times a rock or big piece of ice get wedged between the rotor and the frame...locking up the rotor. Remove this obstruction and you might have cured the problem.
2. You may have a belt that came off and is stuck between the pulleys and the frame. This will lock up the rotor. You will need to get the belt replaced and make sure that it is on correctly.
3. an idler pulley may have locked up (bearing gone bad) and is not turning. Causing the belt to not turn correctly. The screeching is the belt trying to turn on a bad bearing.
4. The belt chamber sometimes gets full of ice and snow...causing the belt not to turn correctly. Remove the belt cover and clean out any accumulated ice or snow.
I hope this gives you something to go on.
Please click "ACCEPT" or I won't get paid.You may also consider sending a bonus if I have been helpful, Please leave positive feedback this is how I'm rated. Thank