Desktop Background disappears at Startup (every time)

Hi,

So I have a MacBook Pro (Retina, 15-inch, Mid 2014) and every time I start my computer my computer will revert back to the original stock photo, you know, the one with the mountains. Then a few seconds later it will go completely blue... I've had so many issues with this computer since day one. It's actually quite disappointing. Every time I go in to get it fixed another issue will occur in addition to my original problem. I've probably been to the apple store over 3/4 times, anyway that's not the point. The issue I'm having now is, once I set my new desktop background (the image I want) and then move it's location to a different picture folder the background will disappear on the next start-up. How do I keep my new desktop image and be able to move that image to another folder without the desktop image disappearing?

Does anyone know how to fix this?

Thanks!