removed my Raspberrypi but plugged in 12 power by mistake. I don't have the regulator installed for stand alone
Now the display only show solid white boxes on the top row. Looks like I cant get into the rspi anymore too. Bad day working on this.
I would suggest adjusting the LCD pot. I had a similar "problem". I tested the board out using the RPi micro USB and adjusted the LCD pot to nice and viewable. When I switched to powering directly from the HM, the screen was blank(ish). I too thought I had fried something until I adjust the pot again.