Homebutton not working, ribbon and dockconnector already replaced.

Since I softly dropped my iPhone 4, the homebutton is not working anymore. I have already replaced the homebutton ribbon and the complete dockconnector.

Unfortunately the problem does still exist, does anyone have an solution? I am afraid the problem is on the mainboard itself, the front and the back are still in good condition after the drop.

I hope someone could help me out.