System crashed and not rebooting


Jan 30, 2019
My system crashed today and then the phone tried to reboot but is stuck eternally in the boot screen with the Mi and Android logo. I only had 100 MB free space, so maybe the system cannot boot because of that? I tried to clear caches with fastboot but it says "device is locked. Cannot erase". Also flashing TWRP is not possible. When trying to start adb shell it only says "error: closed". The newest version of Mi PC Suite cannot connect and an older MiPhoneAssistant version is only able to flash the ROM.

So I really tried a lot, but maybe someone has another idea with which I don't lose my data?