White screen on Laptop but normal with external monitor.

I have a Dell laptop that has a white screen from the moment it turns on. It started doing this after we changed the resolution. I connected it to an external monitor and it works through it. I also opened it and looked at the wires which look to be good. The interesting thing is that after a few hours (about 5) of being plugged into the external monitor, the laptop screen started to work again. But when we unplug it from the external monitor it went white. I plugged it in to see if the screen comes back in a few hours.

Does anyone have an idea of what might be wrong with it?

Thanks in advance.