Today I'm pretty sure I've cornered what the problem is, in fact it is likely there is nothing wrong with the phone, even with Denim. It's the SD Card. Although my other 1520 had no problem with the same SD card, the new phone didn't seem to like it. I figured it out when I went to settings with the SD Card in, under storage sense the SD Card wasn't present. Xbox music sometimes said the music files are corrupted, or came up with some other error. And then I would reboot the phone and that's where it wouldn't turn back on. Today I reformatted the SD Card and I haven't had any problems yet. It's amazing what a goofed up SD Card can do to a perfectly good phone.