Screen Isn't Isnt working, isnt the actual screen itself.

So i've tried to find similar problems to mine else where but the only suggestions were to change out the actual screen. That was the first thing I did but It still would not work, In fact I swapped the entire mother board with another gameboy and the screen did work and the other gameboy i switched to was now not working. I have sound and power but the screen just does not do anything. No flash, no lines, nothing. I do not really know what to do as i am extremely new to the hobby of repairing electronics and my electronics knowledge is very limited.