Car heater

I have a 2000 saturn sl. And the other day when it got really cold for the first time I started my car and it made a squeaky noise, which I know is probably the belt. After that it started smelling like burnt plastic and about five minutes later the squeak stopped. And now for some reason my heat doesn't work. It worked all through the fall, but as soon as it was about 10 degrees it stopped. I put more coolant in it, but didn't help.