2001 Intrepid Brake Issues

I am having problems with the brakes on my 2001 Dodge Intrepid. I reside in Wisconsin and at the begining of Winter 2010 my brakes started acting up. When the problem started I would hear a hissing sound emitting from the brake pedal as if I had air shocks. When it is very cold outside; I'd say about 25 degrees or lower, the brakes will partially work or not work at all. Sometimes when I pressed down on the brakes it feels as if I was pressing down on a concrete surface. I've discovered that after I park my Intrepid in the garage or a warm place the brakes begin to work better. The brakes usually start acting up when the Intrepid is parked outside over a long period of time while I'm at work. Also, ocassionally the brake lamps will remain illuminated and my crusie control wont work. Any help or suggestions will be greatly appreciated.