Heater problems...
Take off the radiator cap (after the car is cool/cold) and look in with a flashlight, see if the coolant has the consistancy of paste, if it does, it's screwed, and you'll need to flush the whole cooling system, and possibly replace the radiator if flushing doesn't get all that crap out of there
I had the same problem with my 97 blazer, the coolant turned to sludge, and no heat, had to flush the whole system, then it worked fine

