Any way you cab double check the PI is actually booting? I've seen a few instances of cards becoming corrupted after updating, and had a dodgy one myself. Worth a check!
Did you try the DSI cable with the text on the inside of the loop? I think the blue end then goes in the driver board with the contacts facing upwards. This seems like voodoo because the cable should function the same either way, but it's apparently fixed a few problems... it probably is voodoo!
Can you SSH or otherwise into the Pi to try some diagnostic steps to see if the display is being detected at all?
Also can you see a faint picture. I've seen a couple of instances of the backlight not firing up, which until close inspection also looks like a totally dead display.
Sorry to drag you through a list of debugging steps, but it's all I can do at the moment!