Why is the screen white and nook does not respond?

Last week I used my nook as usually, turned it off and stored it. But three days after when I wanted to use it again, I founded out that the screen was all white.

I tried turning it on by pressing only the back button, the menu (letter n) + power buttons, and even charging and connecting it to my PC for several hours.

The PC does recognize my nook, but only as a storage device as the screen remains completely white.

Help please! I do not live in the US so I cannot get it to B & N :'(