Hey draakko,
Did you find an answer?
First of all is your screen turning on? Remove the flash from the camera and try to cycle screen infos with DISP BACK button.
You also should know that when attaching a flash, you should disable PREVIEW WHITE BALANCE/EXPOSURE and maybe NATURAL LIVE VIEW too because as you connect your flash, your camera is setting the exposure triangle according to the flash that is very bright and there's a big chance the screen turns black when live viewing because of that PREVIEW EXPOSURE. To explain, the live view is very underexposed but the picture will not. So if you want to live view, you need to disable that setting that is affecting well, the live view.
Hope that helps.
