Connected C-Wire to new Smart Thermostat and Furnace board and still no power
The thermostat you posted has no common terminal (C). The blue wire that should be wired to common at the thermostat is cut off and wrapped around the harness.

You show red, white, yellow, and green wired to R,W,Y,G terminals on the thermostat, but there is no common terminal on that thermostat and the blue wire that should be wired to common is unused at the thermostat yet wired to common at the air handler.

Is there 24 volts at the air handler low voltage terminals (R and C)?
You should, if not check for the door panel switch being closed. It must be closed or tape the switch closed if trying to work with the door open.

The circuit board in the air handler's circuit board should have an automotive type 3 amp fuse:  it may be bad.  If not and the breakers are on and proper voltage is to the furnace, then the transformer is bad.

If you switch the fan on does the fan work?  If so this proves you have both high voltage and 24 volt low voltage control power available.  The thermostat you show has no provision for the common side of power and looks to be battery powered.  Perhaps a Maple Chase brand thermostat?