upload problem -- windows 10 -- uno

Totally new on arduino I tried to upload the blink example -- but I always get the error 'Problem beim Hochladen auf das Board' (German) = problem at uploading

  • The com-port is set on com4 on both sides, W10 is confirming the connection.
  • The board is correctly set to UNO.
  • The green On-LED on the board is on.
  • Another yellow LED is blinking.

What could be the problem? Many thanks for help!

addition:
there is a message 'avrdude: ser_open(): can't open device "\.\COM1": Das System kann die angegebene Datei nicht finden. (German --> the system can not find the specified file).
Why COM1 ??? (The port is set to COM4)

Did you select the correct port from Tools -> Port menu? If that's set to COM4, it should not be trying to use COM1...

tools - port is set to com4 !

After another restart of arduino it works for now (I did restart of the whole windows before without success).

If I run into the same problem again I come back here -- thanks!