My serial monitor window opens frozen, without any output or possibility to input, or even activate the window. Sketch is very simple, but behavior is same even with empty sketch, so I assume problem is not in sketch. I also checked if sketch is uploaded correctly by uploading simple sketch with blinking diode, which worked.

Same behavior with Arduino Nano and Uno.

I tried to reinstall IDE, uninstalled, removed and reinstalled serial driver (ch340) with no success.

I can see Serial monitor window only on windows taskbar, it won't activate after click.

Until now I haven't had any significant problems with IDE or serial monitor for years.

window state

  • Is it uploading at all?
    – timemage
    Commented Feb 16, 2021 at 17:07
  • 1
    Yes, sketch is correctly uploaded, I tried to upload another simple sketch with blinking LED, which worked.
    – pavokraj
    Commented Feb 16, 2021 at 17:13
  • IDE version? Did you get it through the website or the windows store? If you get it from the website, which file did you use?
    – timemage
    Commented Feb 16, 2021 at 17:26
  • 1
    I got it from windows store, version is 1.8.13 (Windows Store
    – pavokraj
    Commented Feb 16, 2021 at 17:35
  • Do you anything plugged in or connected to the Arduino besides the USB cable to the PC?
    – timemage
    Commented Feb 16, 2021 at 17:49

2 Answers 2


Try updating the java. Also check whether the device manager shows the USB serial port without any yellow warning sign on it. If there is a current short in the usb port that specific port will be off for safety, restarting the computer should resolve that problem.

  • Until now I haven't had Java installed, no change in behavior after installation. I restarted computer many times in the process. Driver is correctly installed, and device in device manager is working correctly both with old and new driver.
    – pavokraj
    Commented Feb 17, 2021 at 7:41
  • The IDE runs on a JVM bundled with the IDE.
    – timemage
    Commented Feb 17, 2021 at 12:08

Unfortunaltely, nothing worked, and after hours of trying and googling I reinstalled windows, and now Serial Monitor works correctly.

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