[frostschutz]

You should write a known-to-be-good image to the card (and maybe tell us how you are doing this exactly, which programs / commands / steps etc.).

Also verify that it has been written correctly (sometimes there are faulty cardreaders / USB hubs / etc. on PC, too - or even new SD cards can be faulty).

I don't know what software there is in Windows to do this, in Linux you can use dd to write the image, and cmp to read-compare-verify it.

Then if setting up WiFi or whatever does not work, sometimes this is a router issue, but as long as the device exports storage to USB, you should be able to do offline registration (KoboReader.sqlite) and/or update firmware version to latest by dropping the KoboRoot.tgz onto the user partition directly.

If all else fails you should be able to add some debug scripts to the Kobo rootfs, like a dd read test of the mmcblk0 sdcard device. Or use PC cardreader to get mods like KSM + KoReader etc. going, circumventing the Kobo nickel platform almost entirely, if that is what is causing the issues.

As long as you have access to the SD card there's a lot of ways to handle a misbehaving device. It's hard to imagine a specific hardware fault. I mean sure, wifi chip could go bad or whatever, but still... you should decide that this is the case only after you've confirmed it (if the router is seeing a connection attempt from Kobo, it might not be setup correctly but hardware itself should be confirmed to work).