I hit the power on my furnace and the board hums for a few seconds and then blinks three times . Ihave checked for blockage in vent and is fine. Ihave blowed pressure switch and it clicks is it the switch board or air blower that won't start.

Is it the board humming or the vent motor??

The board

And nothing is running? Doe you have 110 volts to the vent motor? Do you have 24 volts between c and w on the board?

Just checked vent motor has power was testing pressure switch and furnace started working

Odd, usually the vent motor will start even when the pressure switch does not work or does not have power