you have to be sure to change the dip switch, then boot up the machine. i believe the 4 dip switches on the last switchbank
(sw202) should be "off on off off" or if it's still upside down, "off on on off"
but you have to do the change while the machine is off and then boot it up.
your 2nd screen should be plugged into the lower DVI with either a DVI cable, or a DVI to VGA adapter.