XT890 doesn't start at all.

Hello. This morning I've turned off the alarm, turned on WIFI and went back to sleep. I can't tell for sure, but I think the battery was low. During the next 2 hours I checked the time several times. I don't remember accepting any OTA. Eventually I got up, tried to check the time and the phone was off. I tried to turn it on, no effect. No matter how many times and for how long I pressed and held the power button, the green LED only flashed for a split second and that's all. I plugged in the charger, and the LED stayed lit -but- there was this barely noticeable flickering. Charged it for about 30, 60, 120 minutes, didn't start plugged or unplugged. I went to work, 8 hours later (phone was unplugged) I tried to turn it on again, this time the LED doesn't even flash, but when charging there is no flickering. No combination of buttons works. Windows doesn't find the device, neither does RSD.
I've never done anything 'custom' to the phone. The last change I made was setting the alarm to turn off by shaking (yesterday, never used this option before).
Is it dead? :(