I seem to have a very similar problem to what has been discussed here. The USB connector broke off from the LiPo charging unit after a couple of hours use (seems to have had a cold joint) and I decided to try and fix it. I managed to solder it back on, and the battery can now be successfully charged, however now I’m getting the blank screen issue as described. I can hear the sound, and after a couple of attempts at resetting it (holding button C) I was able to get to the game loader screen, but then it went blank again as soon as I tried to load a game.
Now the device intermittently works after taking it apart and putting it back again.
Could you please help check for any bad connections? Any help is highly appreciated.