Lost video input (solved)

I have a standard two monitor setup. Primary is connected via HDMI and secondary via DP, both to my Radeon RX 580. This morning the secondary suddenly stopped working with the message “no video input detected”.

I’ve ruled out the monitor itself being broken, because I tested it with the HDMI cable from the primary and it worked fine. Unfortunately my primary doesn’t have a DP port so I was unable to test the DP cable in it. Therefore, for now, I have a new DP cable on order in the hope that it was just the cable going bad.

I’ve also just run the benchmark utility in Assassin’s Creed Valhalla on high settings and it ran just fine, with no GPU overheating. Therefore I think I can probably rule out GPU or PSU failure?

Pending the arrival of the new DP cable for more testing later today, is there anything else I can do to rule anything out?

I’ll just list the obvious tests which of course you already did, without mentioning them here because they are so super-obvious.

  • Have you tried rebooting?
  • Have you gone into Display settings and verified that only a single monitor is listed?
  • Have you pressed Windows key + P and verified that you can’t select ‘Duplicate’ or ‘Extend’?

If you can answer all three with ‘yes’, my apologies for wasting your time.
If not, I would strongly advise you to do this; it could be a hiccup in the system, which just requires some reassurance that you have 2 monitors. From reading your post, I can’t rule out that you just pressed windows+P twice while looking intently at screen 1, without noticing a screen select overlay which appeared for 10 seconds on screen 2 before shutting off one of your screens. Reboot first, because after disconnecting and reconnecting cables, display detection may be less than 100% effective.

Sorry - I wasted your time, technically! I should have said that yes, I tried those things. Windows only shows a single monitor now, in fact the display settings has hidden any options relating to multiple monitors.

I should also have added that I’ve tried booting into Linux on the same PC, with exactly the same result; the monitor is not detected at all. So definitely a hardware issue rather than software. Of course I have tried connecting the DP cable into other ports on the GPU too.

At this point I’m hoping it’s the cable itself. It was just a cheap “Amazon Basics” thing. I’ll know for sure later today when the new cable arrives.

Edit: Ah my mistake (again), I left the cable unplugged. With the cable plugged in Windows thinks the monitor is there and tries to extend the desktop to it (I can move the pointer off the main display). But the monitor itself insists there’s no input.

FFS. Right as my replacement cable arrived, my monitor started working again.

The solution, for anyone interested: obviously I’ve been scouring the Web for solutions all day, and just now I happened upon one that actually worked. I switched off the monitor and unplugged it from the socket for one minute. Then I reconnected it, switched off my main monitor (the one that always worked), and booted the PC with just the secondary monitor switched on. It just worked! I have no idea why; the blog post I found offered no explanation.

Oh well. At least it’s working, and now I have a spare cable…