OK. Turn off, make sure any jumpers are removed (that should enable the board).
Hold down both mouse butons, turn on, try the "Expansion board Diagnostic" to see if the board is recognized (all that is revealed is whether a board with a manufacturer ID is seen).
Board ID should be 4626/24 or similar. That means it's recognized and should work from that boot.
The reason for the jumper is too high a speed is set, the computer can't boot, and you want to try adusting with the board switched off.
EDIT: The jumper is labelled "MapROM" if that helps you to find it. On this particular model, it just turns the whole expansion on or off IIRC.