icons can barely be seen screen dark

I have a iphone 3g,went to change home button because it was sticking,when i put it back together notice the screen was white.took the screen off put on new lcd and same problem,tried it again, this time the screen started going dark,when i took off screen i noticed one of the screws that holds the logic board had come out and was laying next to the board.when i put that logic board in another housing same problem. is there something that may have gotten fried on the logic board I cant figure this one out.