Black/Flashing Screen on one Monitor, not the Other, after move and Windows 10 Update

[TreeSearcher]

My HP w2207h monitor was working fine with an HDMI connection to my PC until I reconnected my equipment after rearranging my home office and I got the latest Windows Update. Now, when I turn on my PC (a Dell XPS 8700 with an nVidia GNV8T graphics card), the PC logo comes on briefly, the screen goes dark, and an error message flashes on the monitor too fast for me to read it or even grab a photo before the screen goes dark again. I tried another monitor--my HP 2159m--with the same tower, and it works fine, but only using the VGA port in the graphics card, not HDMI. I tried connecting the first monitor to the same VGA port--nothing. I've been wanting to hook up both monitors to the same tower and connected the first monitor to the HDMI port in the graphics card while the second was connected via the VGA port, but then the second screen shows only the Windows 10 background and no program icons, while the first screen is black. I tried the onboard HDMI port just in case, but nothing.

I've read what troubleshooting tips I can find online in the HP community, the Dell community, and elsewhere, and I've found suggestions for turning on the PC in Safe Mode, which I haven't been able to get to work, and for updating the BIOS, but I've found nothing that addresses what happens when I plug in both monitors. I'm reluctant to update the BIOS if I don't have to (I'd have to download the update to a flash drive attached to my laptop) or open the PC chassis to check the graphics card if there's a simpler fix. Once again, the PC and first monitor were in daily use and working just fine until recently.

I've also noticed that when I turn on the PC with the first monitor connected, the Num Lock key stays on, and I can't get it to unlock. No idea if that's related to the monitor issue.

I'll check with Dell, too, but thought the difference in how the two HP monitors respond might offer a clue. Hoping for HELP!

[TreeSearcher]

An update: More info, but no change in situation.

I made a mistake on the graphics card. It is NVIDIA GTX745.

I've tried two HDMI cables with the same result for each.

I ran a full SupportAssist diagnosis on the Dell PC. All is fine.

I have the latest drivers installed and BIOS version.

Is there any reason to think that the HP w2207h monitor is part of the problem? I do get a few flashing images on it using the HDMI graphics card port before the screen goes black. That still doesn't tell me why I get an image on he other monitor via VGA and a black screen via the same HDMI port.

I've had a couple suggestions from the Dell Community, but the only things I haven't tried are a third, new HDMI cable and opening up the PC case to check the graphics card seating. 

Thoughts?

[Echo_Lake]

@TreeSearcher

Thank you for posting on the HP Support Community.

Don't worry as I'll be glad to help, however, to provide an accurate resolution, I need a few more details:

• Did this happen after a recent window or software update?
• Have you made any hardware/software changes?

While you respond to that, let's try these steps: 

• Note Before you begin: Turn off the computer.
• And disconnect all connected devices from the computer except the mouse and keyboard. This includes removing thumb drives and camera-type memory cards.

Step 1: Checking the power

Step 2: Displaying a built-in on-screen message

Step 3: Fixing a bad video connection

Step 4: Testing the video connection

Step 4: Connecting the monitor to a different computer (do not skip any troubleshooting steps even if you feel steps are repeating)

• Use the steps in this document: https://support.hp.com/us-en/product/hp-value-23-inch-displays/7274744/model/10402854/document/c0129... to resolve this issue or to determine if the monitor is defective.

Hope this helps! Keep me posted for further assistance.
Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution.

[TreeSearcher]

Thanks; I'll try this soon.