Yesterday, after having my phone in my pocket for the whole day, not checking it for hours, it just had a black screen in the end. At first i thought the battery had run out, so as soon as I was home, I plugged the phone in. It did not load at all, though, and there was no light telling me the phone was loading. I let the phone just lie around over night, thinking the charger cable was just damaged, and used another one the next day. It charged without problems, as normal. When it reached 66%, I decided to turn the phone on. Holding the power button resulted in a light vibration, as always, and the screen just going black (it showed the battery with the amount charged in it before) The lamp that showed me it was charging went off, too.
I had similar problems in the past, but those could be resolved without a problem with holding the volume down + power button for some time, which rebooted the device. This does not seem to work now, though.
As my PC won't recognise the handy beeing plugged in, I can't tell you what version my handy is on exaactly, but I can tell you that I only some days ago received notification about a software update, which I had not yet installed. Before that, the software was on the latest version.
Is this a known problem? All I could find where instances where this problem was fixed with holding the volume and power button.