I can't see in your post you checked the video cable/connection.
This morning when i turned on my old desktop computer, my acer LCD monitor was displayed nothing. The only thing i can see is the light on the bottom of the LCD keep flashing. Normally, last time when i pushed the power button i can see the acer logo appeared on the LCD screen but now no more acer logo appear, it just no response. My pc can POST with a single beep sound and i can heard the melody when my computer enter windows. what happen to my computer?