iPhone 4 is not rotating to landscape mode

Hello,

My iPhone 4 does not rotate anymore, but after I lightly "slap" my iPhone it is rotating again.

But the weird part for me is if I play a game wich needs you to tilt the iPhone in order to steer, that strangely does work.

I do not have the rotate-lock turned on so this is not the problem.

I did notice when I first opened this iPhone it was missing the motherboard shield wich covers the accelerometer.

After I placed a new shield on it the screen is turning, only after I lightly slap it, but after a few hours I have to slap it again in order for it to work.

Before I placed the shield on the motherboard it would't turn at all.

please help.

kind regard.