Uploading works, BUT no Serial Communication possible?

Hey Guys,

I need some help!

The Arduino Pro Micro is connected via the on board USB Port to my computer. My problem is, that the Arduino is not able to communicate with the computer, when in running mode.
This means, that I can Upload a Sketch after resetting the Arduino by connecting RST+GND. And the program is running perfektly.

BUT after the Arduino is not longer in the bootloader, the computer looses connection and is recognizing the Arduino as "Unknown Device".
I can not see the Arduino Port in the IDE.
After pressing Reset again, the detection works. The Pro Micro appears on COM5.

My biggest problem is, that I can not open the Serial Monitor to observe any ouputs.

Got anybody an idea???

Iam working with:

Arduino Pro Micro.
Windows 7 -64bit.
Arduino 1.6.13.