First let me say I love a good game of chess myself. Scotch as White, Scandi as Black, lol. Now as for your phone, I had the same problem with a Galaxy Trend TWICE, and it turned out to be a faulty power button. Phone would turn itself on during the night, and then when I wanted to turn it on during the day I couldn't!!! It was under warranty so I took it in TWICE to get it fixed. Doesn't say a whole lot for the Trend, but it seems to work now! Not saying it's what you have going on, but eliminating the other two suggestions it seems possible for sure!