Hi Antikx,
this prooves what I didn't want to believe myself but others suggested: That the 3100 and 1000 NAND backups are not interchangeable.
I am sorry to hear that you have troubles with the NAND restore. I hope you know that this was neither my intention nor did I even see that you have a C1000. Thought you have a 3100, too, otherwise I would have warned you.
On some kinds of PDAs it helps to let it sit for a while without any battery or AC. Maybe try this over night, then, as the first action, press D+M and insert the battery.
AFAIK the diag menu is NOT overwritten by a NAND restore, so it should still be there.
Can you get into the other boot options, such as OK+ON flash menu or D+B emergency system?
daniel