2004 Toyota Corolla My Heater Wont Work

You can buy a coolant tester from most autoparts stores for $5. Test coolant in radiator or coolant recovery tank (radiator is best), coolant should test at least -30F.

If original coolant (Toyota coolant is red in color), it should be changed every 24000 miles.

Next check heater core hoses, both should be hot at operating temp. If not hot, then thermostat.
If hot, then divertor valve.

Best advice is to get car into garage to thaw and then see if heater works, if it does, then get coolant flushed and changed, DO NOT let this engine overheat.