My thermostat won't turn on even after changing the batteries. What's wrong?

You are supplying conflicting information. You say that the thermostat won't turn on. Then you say that your roomate got the heat to turn on. Which is it? Look at the window on your thermostat. If it is dark then you will know that the thermostat is off. There are two possible fixes. First check your circuit breakers located inside of your house or apartment. If the heater circuit breaker is "tripped" reset it. The heater and thermostat are controlled with a simple plug. Check to make sure that you have not lost the connection between the heater and the wall plug. If your thermostat has any light at all on the face, you have a bad thermostat. I had this problem. Most thermostats available at your local home improvement store are universal. They are priced around $30. They are reasonably easy to install. Here is a third consideration. If you have central heating and air conditioning you will have a heat pump located outside. You will see a fan blade at the top. In hard water areas it is typical for this fan to freeze up. A simple insertion of a long screwdriver to tap on the fan blade may solve your problem. Good luck.