My furnace won't turn on the pilot light is lit but no heat it is old and cannot afford a new one could it be the coupler I had it replaced once before

Why won't it go on

Have you checked for power? Is the door off? is the tstat set correctly?
If the pilot light is lite,your thermocoupler is probably OK
Does it make any noises when the tstat is turned up?or is there nothing?
Be sure to check for power make sure the breaker is set, some have a on-off toggle on or near the outside of the furnace, double check