hyng WROTE:
I have just tried to supply input voltage less than 6V to PR23, and the result is quite similar to yours. The buzzer will be ON for a while when the robot is switched ON which is normal but the LCD show nothing. So i am assuming that the root cause is from the input voltage if referring to the photo you have attached.
The input voltage must be at least 7V for the regulator to generate 5V but remember that motor power should not more than 6V. I guess you need to try increasing the input voltage.
Thank you very much for your help & sorry for my mistake wrongly swap the battery...my robot is work properly now.Thanks for all of you again!