@kaninkalle
Provided there is no hardware fault, there is likely still a file onboard which is preventing the device booting. If you don't wish to go thru further 'trial & error' file removal to find the culprit then simply reformat it using only [Only registered and activated users can see links. ] with correct settings while it has Cure firmware loaded.

About point 7 and the V2.70 firmware file you loaded: I don't quite understand what you've done but if it was placed in the device as GUPDATE.GCD it won't be used to update the device until it next boots fully. In any case, you don't want original fw loaded yet as only cure fw can re-enable Mass Storage Mode in a soft-bricked device by preventing files being loaded during the boot.

About point 9: You clearly can reach preboot as you've loaded a cure fw RGN file.