What is wrong with my computer, monitor, and\or video cable?
 

https://ecomodder.com/forum/attachme...1&d=1540280217
Dell XPS 8900 that I bought about two years ago.
The only change that I have recently made to my computer was unplugging the monitor from the on-board video to the video card that came from the factory. The screen started going black for a second or less, but I do not know which happened first. This is the second time that I tried to wake my computer, the power light comes on the case, the Num Lock light turns on the keyboard, and the fan starts spinning, and the monitor goes back to sleep.
When this happened before I turned off the power and it booted up just fine, but I do not want to do that again if I do not need to. If I need to do a proper shutdown each time that I would normally put it to sleep then I will, but I want to fix the actual problem.
Keen observers will note that the monitor is not asleep. Good eye! I have another monitor in the garage, but I am not sure where. The monitor does not have HDMI out, I have a DVI to HDMI cable, and I do not have another one that I can try. I did plug the monitor into my laptop and it worked, but it had all of those green pixels, which were not on my laptop's screen.
What should I do next?
Thanks! :)

Don't know I understand your problem description accurately.

That said, I'd start with BIOS and video driver (both the on-board and discrete) updates. Problems due to sleep mode are common, and often fixed in updated BIOS versions.

So, do a hard restart?

Download the Dell Command Update and install it (first check if it's already installed). Run the utility to see what BIOS (UEFI) and video drivers exist, and if you're curious what the new BIOS version fixes, click the button to get more info.

My Dell laptop was having display issues after waking up from sleep, but it was fixed by a BIOS update.

For me all modern monitors are a problem impossible to solve, since 99,9% uses LCD technology (LEDs are LCD with LED backlight).

Have you tried to plug it in another PC ?

Don't get All Darc started. He will have you throw the monitors out a window as part of "troubleshooting".

All Darc- Wish I could have shipped you the thousands of CRTs I've tossed out over the course of my career. I might have a couple sitting around somewhere.

Come-on...
I did a joke but also made a tip : "Test the monitor in another computer."

;)

That “black isn’t black” issue is common my work screen looks that way.
I was told once it was a bandwidth issue but it turned out to be a failing switchbox

using a different cable or a different type altogether (use vga or dvi instead) might help.

Wait, Xist. You aren't using a VGA cable are you? That is an analog standard. Use DVI, HDMI, or DisplayPort. Anyhow, have you updated your computer yet?