Lines Blocking Mac Screen

After lending out my MacBook Pro, I have turned it on to find there are wide lines covering the screen to the point where I can't use it. When I plug it into a monitor screen I can use it via that but it's unusable by itself.

There has been no mention of any physical damage to the laptop. I need advice on what could've caused it and how to fix it please? Any thoughts would be really appreciated!

This is all I can see when turning on the MacBook: