D-Sub no signal: monitor keeps going into power saving mode

LP
I just powered up my PC after letting it sit idle for about a month—and what do I see? A "D-Sub No Signal" message on the screen before it immediately kicks into power-saving mode. It’s as if the computer and the monitor have completely forgotten how to talk to one another! Does anyone have any advice on how to troubleshoot this connection issue?

Did you double-check that the VGA cable is actually seated properly? If your monitor has any other ports besides VGA—which, let’s be honest, most modern ones do—you should probably dive into the monitor's own menu settings and make sure the D-Sub input is actually selected.

With certain General Electric monitor models, I’ve seen people fix this specific error just by power cycling the unit. You turn it off, flip it back on, and it usually manages to auto-detect which input the graphics card is actually running through.

If you're dealing with an Apple monitor, you'll pretty much have to (re)program the DDC chip on the circuit board itself.

The cables are seated perfectly—I've double-checked the connections, and since everything runs flawlessly on one PC, I know they aren't loose. However, I'm getting that error message on the other two machines. It’s an Apple's monitor in question, and there isn't any other input being used at all.