Solved:
@Lakotaubp yes, the installer was the problem.
I used 0.1.13 which is linked here:
https://devices.ubuntu-touch.io/device/hammerhead

This version has the bug. Then I downloaded 0.1.20 from Github:
https://github.com/ubports/ubports-installer/releases/tag/0.1.20-beta

This one seems to be working. Now I have Ubuntu Touch 16.04 on the Nexus 5 !

Thanks for your support

Thanks @Lakotaubp
I tried 4 USB-Ports and 3 cables. Always the same problem.
Then I tried another PC with USB3-Ports. The first one only had USB2.

Now I could reach the step Pushing files to device.
There I get this adb push error

Could this be a bug in the installer? There is a strange combination of '' and '/' in the file path.

The mentioned file is existing in the correct path (with '')

Edit: This forum does not accept the backslash sign.
...There is a strange combination of Backslash and Slash in the file path.
The mentioned file is existing in the correct path (with Backslashes)

Hi,
I had the same situation like the first black screenshot posted here.
I am using Nexus 5 with latest stock Android and Windows 7 on PC.

I could get into bootloader mode with Poweer+Vol-(-)

When starting UBports installer, while device in bootloader mode, I came one step further.

UBports Recovery started on device

UBports installer on PC shows "Waiting for device to enter recovery mode"

...this situation is unchanged since about an hour.
What can I do?

best regards
clic