So i bricked that Device and erased the Nand by trying to get Debian onto it.
Then i took of the Harddrive and connected it to the PC and since i was booted on Windows, it formated it new.
In some Forums i found ot that it cant be bricked since it can boot from SATA.
So i found this Topic (viewtopic.php?f=55&t=2146) and followed it. With the UART Bridge i could see the Boot process and it booted the U-Boot but it said that the Nand was corrupted (BAD MAGIC NUMBER).
And the rootfs booted too till some point. It said Kernelpanic. I tried other rootfs too some said the same, some didnt boot at all and some said the kernel was too old.
So if someone has any suggestion how to put (debian/arch/any other linux distribution) or even the original firmware on it, that would help a lot.