Is your volume cranked up to maximum?
My Picade has a Pi3 with the standard Pi power supply and 8 inch screen and if I turn the volume up past about 80% I lose the screen until the volume is turned back down again - then the screen leaps back to life.
You might also like to try a separate power supply direct to the screen - does the LED on the button board light up if you do that? If not, then I'm guessing you've unfortunately got a bad screen.