I've been struggling with mine all morning with the same issue.
Mine would not wake up from sleep (will just white screen).
It will boot using a hard reset (i.e. the power button and volume down button being held down for 8 or so secs). I restored and synced it multiple times but it still has a problem waking up and just just goes to white screen.
I saw a post suggesting a loose connection which I had my doubts about (as it will wake with hard reset) - bit BINGO! If I wake mine (with index finger) whilst applying pressure to the top of the screen area (with my thumbs) it will wake up. When I become frustrated enough I'll take it apart and see if something has become loose.
Hope this helps.