Remove the cover for the high volt inlet to the furnace, there will be 3 wire nuts inside 2 high volts and 1 ground.

Test for 115 volt there inside the wire nuts

if you have 115 volts there then the wire between the board and the power inlet are bad, Replace those wires now. 

If you do not have 115 volts there move over to the switch for the furnace.

Verify that the switch to the furnace is on.

Remove the cover to the switch and test for 115 volts coming into it.

If you have 115 volts there, you need to replace that wall switch.

If there is no 115 volts there, then we have no power to the attic unit at all from breaker.

Go outside or to the garage, find the electrical breaker panel and remove the cover.

Now find the breaker labeled fau and test for 115 volts leaving it.

If you do have 115 volts and you’re sure you have the right breaker, then the wire from the furnace to the electrical panel is bad and needs replaced. This is a job for an electrician.

No power is leaving the breaker, turn it all the way off and then back on.

If power starts leaving the breaker again and furnace turns on, watch system to see if you can find the reason the breaker tripped. If no reason can be found it is possible for a power surge or an isolated incident to trip a breaker.

If power still will not leave the breaker even after resetting it, it need replaced. You need a new breaker. We can advise you through an air conditioner but for going into the main electrical panel, leave that to a professional electrician. So Contact somebody with the proper licensing.

If you already have your breaker fixed and power is heading back to the furnace then restart the matrix now to be sure there are no more problems.