Display off

Hi,

I have a problem with my Lumia 800.
Unfortunately it dropped out of my hands and got some marks on the edges, however worked fine throughout the day.
After the battery ran out I connected it back to charge but since then the display is off. The phone reacts on the buttons (vibrating) but the display doesn't come up and stays dark.

Any ideas what might bring it back to life?

Have you tried a soft reset? Just hold the power button down for about 30 seconds.

Also, computer recognizes it when plugged in. I can sync.
It's just the display.
How can that be if it all worked fine before battery ran out?