Not sure how to resolve MacBook issue!!!!

Hi all,

I’m in a huge pickle here.

My Macbook started to have an issue where it had the below screen all the time which I could live with. The screen just started to go black, but it would still be powered up. I would have to power it down And restart it but the black screen was frequent and would go black randomly. Now, when I turn it on, I have a black screen and padlock Which needs a password - I have no idea what this is and don’t remember it. I have tried to access other screens to test but it still keeps giving me the black screen, plus nothing happens when trying to access menu’s etc that are suggested on other forums.

I’m going to sell it for parts as I’m guessing it’s done. My concern is, I used it for work and I have customer details on my hard drive which of course I don’t want anyone having access to, plus family photos etc. Could the hard drive be accessed by who ever buys it. Any help would be much appreciated!!