Hello, Tam -
The warming element in the coffee maker base may be faulty (no longer working.) Eventually, heating elements can fail.
You do not state the make and model of your coffee maker, nor do you state how old the machine is.
Depending upon whether you wish to test the warming element to determine if it is no longer working or whether you choose to take the machine to an authorized repair center and depending upon the cost of replacing the warming element, you may choose to just purchase a new coffee maker and send the old one to proper electronics recycling.
There is information here on how to test a coffee maker warming element to determine if it is working:
Look for the section headed "Servicing Warming Elements."