What is the meaning of a question mark on my hard drive?

My macbook pro dropped hard on a concrete floor. It refused to come on, I took to an engineer who advised i replace the panel, after replacing the panel with a new one I realised that there was a question mark on the hard disk and no files in it. Please I want to know if the hard disk is damaged? And if it can be repaired to get my files back or I have lost my hard disk and it can't be remedied. Thank you