1 long and 2 short computer beep code error indicates a video error has occurred and the BIOS cannot initialize the video screen to display any additional information.
In my case, my computer has a video card, I simple remove it and clean a little then put it back. Beep is gone after that.
For more Award BIOS Beep codes that can occur, please visit this blog https://www.computerhope.com/beep.htm
