5V coming on for a couple of seconds then going back down means screen is not recognized. Can be various things but first you must eclude a bad LCD/LCD cable. 2013/14 and 2015 are not compatible. 13" to 15"… dunno, sometimes it can work.
If there is backlight, LCD should be recognized, so more likely to be a damaged connector or filter inductor on an eDP line for example.