Arduino Nano --> Sketch Upload does not work

Hi,
i'm not able to upload a Sketch to my Arduino Nano.
The following message appears:

Beim Hochladen des Sketches ist ein Fehler aufgetreten
avrdude: stk500_recv(): programmer is not responding

The strange thing: uploading to my Arduino Mega 2560 works perfectly.
I have tried two other Arduino Nanos (from a amzon set) and None of them works.
So I think I can definitely rule out that the Arduino Nano is defective.

So what else can be the Problem?
I have tried different ports and different chipset-settings with no success.

When i try to get the board Information, the Dialog window says (sorry, german):

BN: Unbekanntes Board (Unknown Board)
VID: 1A86
PID: 7523
SN: Laden Sie irgendeinen Sketch hoch, um sie abzurufen (Upload a Sketch to get the board Information)

But i CAN'T upload a Sketch ;-(

Please help ;-(

Best wishes
Daniel