XPS 14z boot up issue

This is an old laptop, bought in 2012. used few months regularly. While this was occasionally used at home after that, it started to give this error. 

"Check cable connection!"

"PXE - M0F : Exiting Intel PXE ROM."

However, the error has not been persistent but instead the laptop is temperamental. It sometimes boots fine and other times stops at this error while booting. I am guessing it is something to do with loose hard disk connection. Since it was not critical all those years, I let it misbehave. Now in the quarantine world, I need it desperately for kids homeschooling. I have opened the back and the hard disk looks well secured. I don't have a clue what else to look for. Any ideas?