put a monitor back on it that you obviously installed ok with....
after booting into the graphical screen--find the "display" setup and set it to
generic 800x600 monitor
or since the monitor will run 1024x768 set it to
generic monitor 1024x768
it will still work with the original setup and "should" work with the new monitor--
unless the original monitor was a LAPTOP screen, and then it's apples and oranges again.