It sounds like it might be the zoomed text setting in Windows.
From the Downloads page:
If MapForge won’t launch on your PC without locking up or quitting, see the section called “Windows-specific Incompatibility Discovered” in this Kickstarter Update.
If that’s not it, let me know how many Add-Ons you’ve installed and enabled at once.
You can find that preferences file by looking in all three of these places:
Look here:
C:\Users\username\AppData\LocalLow\Adobe\Director 11\MapForge\Prefs\
And here:
C:\Users\username\AppData\Local\Adobe\Director 11\MapForge\Prefs\
And here:
C:\Users\username\AppData\Roaming\Adobe\Director 11\MapForge\Prefs\
(the exact path varies under different versions of Windows, and depends on the compatibility mode you've selected for MapForge on 64-bit Windows)
Rename the “Display.txt” file to something like "NerfedDisplay.txt", then try launching MapForge and see if the problem has gone away. If it has, please post the contents of the "NerfedDisplay.txt" file here, so that I can see try to figure out what might have gone wrong.
By the way, are you using a TV as a monitor?
I had one customer who was doing this, and they had a hard time getting MapForge to run properly, but tweaking some setting on their nVidia card that was driving the TV display suddenly made everything work fine and fast.