[Help] Theme and Desktop

A classmate's phone has a problem. Model: N5000. In the themes for the registered model, the situation shown in the picture occurs (pixels dropping out): a white bar on the top, a white bar on the bottom, and it can't fill the entire screen. I tried several different resolutions, but none could fill it. What's going on? By the way, even though the model is correctly matched, any game over 500K shows 'application software error,' 501 is the same. Is it a memory issue? It's clearly the correct model, and we tried different networks, but it's still the same (we're all poor, can't afford to change the phone). Seeking help, thanks~~