My Nokia Lumia 620 digitizer sleeps but difficult to wake up?

I replaced my lumia 620 digitizer when the original digitizer got cracked.

Now anytime i charged the phone or the phone goes to screen lock i find it difficult to wake it up, even though calls and messages come through however i cannot identify the caller or the sender of the message unless i remove the battery and put it back then restart the phone.

Can anyone with similar problem help or what is the cause of the problem