What I want you to try is to simply remove the png image you inserted into the terrains folder after the complete reinstall.
And you never said that you actually got into the map maker. So I'm rather certain it's the picture itself when you load it.
try making sure that you Height mask is:
513x513 in size
Grayscale and not RGB
One layer only.
Not being one of these is the mast common cause for Mapmaker Crashes
Follow that, if it still doesn't work, make the png image a .bmp then back to .png and it should work.
And no >.> derrpness pl0x rofl, just trying to help