Flashing Amber Light on OptiPlex Desktop

Here's what you do to solve the flashing amber light issue...

Unplug the power cable from the tower. You can just pull it from the back of the computer tower, as it's toward the top. (No need to crawl under the computer table if the computer is on the desk.)

With the power cable unplugged, press and hold the power button for maybe 4 seconds. You won't likely see anything happen.

Now, plug the power cable back in. Depending on that computer's settings, it may book up on its own. If not, just press the power button as normal and it will boot up.

(The amber light is an indication of an under voltage situation. It's a protection measure.)