Heater Went Out and its COLLDDDDD
 

So my heater went out in my dads 99 v6...flushed the system, and all the knobs work, the car shows it heats up but the heater wont work at all. we have no clue what is wrong and was hoping someone could give me a quick fix. any help appreciated thanks

The heater core?

Is there air coming out of the ducts?
Does the air come out of the vent that corresponds to the position of the control knob?
Did the heater work before the flush?

Make sure there are no vacuum leaks from cracked or disconnected hoses.
Make sure there is vacuum getting to the heater control.