My M8 seems to be dead.

Today I went to bed quite late so I changed my alarm clock on my M8 and went to sleep.
I woke up naturaly without to alarm clock so I decided to check the time on the phone. It was off. I got used to this baaaad software that comes with the device, that makes it stop working sometimes (you have to take he battery off and restart the phone). So I took the battery off, plugged it back, and pushed on.
Meizu appeared, and then it went off. It does this sometimes so, I pushed on again, and this time Meizu shwed, but strange white lines appeared after the logo (as if the boot screen was buggy, and then it went back to meizu logo, and so on.
I tried several times and the same stuff happened. I decided to do a registry reset, but the problem still occured after that!
It's not recognized by my pc because it doesn't boot, so I can't reset the firmware... I don't know what to do...

Lothar,

not willing to scare you but look here and here , it sounds like...

Can you boot to upgrade menu? if yes boot to it and then hook onto the pc, you will be able to copy a fw xip.bin to perform an up/downgrade.

And once the problem is solved, maybe you can prevent this turning off issue by installing the Maintain software...