After Screen Fix, Power button works, but can't sleep

After fixing my screen (replacing with a new one), I noticed that my Screen can't go to sleep anymore, even with my Smart Cover. The Sleep button also won't go to sleep, but if held down, it will power off (Slide to Turn Off screen appears). It will also turn on if it's pressed if it's turned off.

However, if power button is pressed, it won't wake up from sleep mode.

Is there anything I could have removed by mistake? The green cable seems to be fine, and if it was cut, the power button wouldn't work at all, am I right?

Please help!