Big thanks to everyone, my phone is booting again. I reflashed the kernel and expect for the overclocking is everything as I lef it before.

So my question is : what to do next ? I still would like to try Nemo, Nitdroid, that is the reason i bought a SD card. I guess I should restore the power-kernel before I try to set up the U-Boot again.

But I am not sure what went wrong last time. To be honest I do not get the steps mentioned in the first post. I just want to try the booting from the SD card, to have the possibility to boot into the power-kernel and to access the backupmenu.

Could anyone give me some hints please ?