Windows 8.1, serial Monitor problem

Hello experts,

I come from Windows Xp, have now 8.1. Newest Arduino-Software is installed. My Arudino is connected via USB with the PC, where I can see it as COM 5. Upload works, serial monitor works.

But: After having used the serial monitor and closing the Arduino-Softare and starting it again, no connection is possible, I get the message, that any other process uses the port. The only way I found is to restart windows. I tried the windows taskmanager to find the process, no success.

Has anybody an idea?

Greetings from Hamburg, Germany