Today, I got another display model. http://wiki.52pi.com/index.php/5-Inch-800x480-HDMI-TFT-LCD-Touch-Screen_SKU:Z-0053
When I replace the previouse work display, it show white screen like you.
First, I found that the HDMI connector is very hard to put in. So, the signal may not send or strong enough. I had put in to the deep end. Then, it show me some shadow of screen. I think, the signal was corrected. It work after reboot.
Second, I move it to another board and supply the power from the USB port on the board. When I switch on, it look like a short circuit, the screen still white. I think, the screen consume much power at the initial time, if the power is not enough, it cannot initialize and then, not work. So, I try to power it with external adapter. Then, it work.