Furnace Fuse Blows Immediately
If you have disconnected all external wires to the control board with only internal wires to the unit connected and the fuse still burns, that very likely indicates a failure of the board.  With the fuse burning quickly, that often means a component in the power supply side of the board has catastrophically failed.  To verify this, you could disconnect all wires to the board except for the power connection and the door switch and test to see if the fuse still burns in that condition (make certain you are using a correctly sized replacement fuse, obviously).

Replacing a board is typically not difficult if you can find a compatible replacement.  Unfortunately, the wholesale price for these is often $200+ or higher.