Geeetech

hello i think there is a short circuit in my Geeetech Sanguinololu Controller board for RepRap Prusa I3 MK8.

I have a geeetech prusa i3 Aluminium from august 2016
And i have done a few prints on it so far. But suddenly it just broke...

When i turn on power, my lcd just show black squares.(all fans spins normal) But it kills my computer. (black screen an it needs do be restarted) thats why i think it maybe sends 12v in usb cable

If i connect only usb to board, lcd works normal and i can connect in repetier-host. so firmware and the rest on the board is ok i guess?

I have disconected every cable and stepper drivers connected to the board exept power in and lcd. I have checked backside of the board to see if anything was shortcircuting.
I have checked v input 11.95

What is wrong??

1.When you turned on power,did you also plug the USB cable?(cuz you said it kills your computer.)
2.Connect only usb to board,lcd works just suggests the lcd is good and you can't do any heating.
3.When you just leave the power cable and LCD plugged,did the lcd work when you turn on the printer?
More details like pictures and videos would be appreciated.

1. Yes it happened while checking the nozzle for flow just before starting a print. Qfter that I turned to the computer and then it was black, and also the lcd. So i shut my printer off and restarted my computer, then when trying to do a new atemt i hae my usb connected and the lcd worked again so i turned on power, and it killed my computer and black square lcd again. I have now measured how much power there is in my usb cable while having it connected to the board with power on. And it shows 9.5v and isn't a USB cable supposed to sen 5v? So i guess there is something that has broken on the board when converting 12 v down to 5...

2 yes

3 no

Pics can be posted later

OK,so your "lcd" means the screen of your computer NOT the LCD panel on the printer?
Have you tried printing it with a SD card?How did it go?

By lcd i ment LCD panel.
LCD panel is not working if i turn on power. Only black squares.
only time LCD panel is working is when only usb is connected to the computer. (Not power conected to 3d printer)