More than likely the radiator fan resistor has gone bad. It is located at the bottom corner of the radiator.
First check the coolant level, a coolant leak would cause a heater to stop working- assuming you mean the blower is blowing but it isn't hot. A stuck thermostat will also cause you problems with your heat.
Yes it can. A faulty thermostat can cause overheating which will cause coolant to be pushed out of the system.
No, low coolant would cause the opposite.
a leak in a head gasket could cause coolant to go into only one cylinder.
The heater will stop getting hot when you're low on coolant. If the coolant is low enough the engine will overheat and it will be severely damaged.
broken radiator
clogged radiator bad water pump bad thermostat fan not working loose belt
water pump, oil, water, engine coolant....main cause would be engine coolant, just check to see if you have a leak.
blown head gasket
troubleshoot the coolant on a 1999 oldsmobile intruge
Leak in heater core
you have to find where the leak is first.