Use a test light to see if the fuse to the blower motor is good, if it is, Make sure the plug is connected at the blower motor, if it is, with the test light check the power at the blower motor itself. You may need to unplug it to be able to check for power. If you have power at the motor connector then remove the blower motor and bench test it. If the blower (squirrel cage) doesn’t spin, you need a new motor. Just so you know, when a blower motor speed rheostat or resistor fails, it defaults to high speed fan until you get it repaired. The fact that you said that the fan worked fine one day and it was completely non-operational the next leads me to think that the blower motor or the connector at the end of the harness have failed.