Thanks, your post motivated me to try to repair my dingoo again, he is lucky that I am so patient
Your hints finally didn't help me, though I found out that I made some mistakes. I found another "a320 recovery tool complete" archive, with a more detailed readme. this: http://pastebin.com/HiQL4Qnn
For example I didn't run the unbrick tool as admin...
Everything seemed fine, I installed the emulators and games again, unplugged it, the update progress bar appeared, though without animated bar. There were the graphical glitches in the menu again, but the menu didn't hang.
BUT, when I reset the dingoo it froze at boot screen. When I reset it with usb plugged in, and then unplugged it, I came to the main menu. This sucked. Same was with some other "Flash files" I found on the internet.
I thought I could still use it with dingux and dualboot. My old mini-sd card seemed corrupt, so I bought a micro-mini-sd adapter. I installed dualboot and opendingux and everything. Seemed to work. But it also started to freeze, at first because of some emulators, which didn't work. Then it didn't start complete. I tried several new dingoo-flash, sd-card-format, copy-everything attempts, also with another card, but always with the same result
I powered it on with select pressed. I reached the opendingux boot screen. After some seconds the Dingoo restarted. When I pressed start to see the console putput the messages were like I have no sd-card inserted.
Funny thing is, I discovered that the boot-up to the default Dingoo system now works again (though it also freezes when I want to access the sd card in the dingoo file navigation).
Maybe it works now because of the dual boot loader. I don't know and I'm curious which strange behaviour the dingoo will show next
If I remove the SD card, the Dingoo freezes at the second paw boot screen... with card inserted, it boots