Couple more things to try on top of what @shizuka already covered:
- Check which GPU is actually active
If you have both a graphics card and motherboard outputs, sometimes Windows flips one of the screens to the integrated GPU. That can cause wrong resolutions or black screens.
- Go into BIOS and look for “Primary Display” or “Init Display First” and set it to PCIe / PEG if you’re using a dedicated GPU.
- Disable “iGPU Multi-Monitor” or similar so the board ports stop confusing things, at least for testing.
- EDID weirdness
When a second monitor plugs in, the GPU reads each monitor’s EDID (the data that tells it what resolutions it supports). Sometimes that gets corrupted or misread.
Try:
- Power down PC completely, unplug it.
- Unplug both monitors from power and PC.
- Wait 30 seconds.
- Plug in one monitor, boot, set it correctly. Shut down.
- Plug in the second, boot again, then set up extend mode and resolutions.
It sounds woo-woo, but I’ve fixed stubborn dual‑display issues this way more than once.
- Try different “primary” monitor
Windows sometimes insists on giving the primary monitor the “good” signal.
- In Display settings, click the monitor you want as main → check “Make this my main display.”
- Sometimes swapping which one is primary suddenly makes the other one stop going black.
- Check power saving / weird monitor settings
On the monitor itself:
- Turn off any “Eco mode,” “Dynamic Contrast,” or “Auto source” features.
- Make sure the input is manually set to HDMI or DP instead of “Auto.” Auto can freak out when another screen is plugged in and suddenly your first monitor acts like it lost signal.
- Watch Windows’ behavior when it breaks
When the one monitor goes black after you plug the second in, open Display settings and see:
- Does Windows still show 2 displays?
- Did the resolution of the black monitor suddenly get changed to something insane, like 640x480 or 75 Hz your panel does not support?
If it did, force it back to its native res and 60 Hz, hit Apply, and see if it comes back. If it instantly reverts to a bad combo, that points to either EDID or a flaky cable/port.
- Post exact hardware
You do not have to, but if you want more targeted help, share:
- GPU model
- Both monitor models
- Which exact ports you are using (e.g. GPU HDMI → monitor HDMI, GPU DP → monitor DP)
Some GPUs share bandwidth between ports and silently downclock / drop one display when the second is attached, so the exact combo actually matters.
You already tried the basics via what @shizuka wrote; at this point I’d specifically suspect: bad EDID, buggy driver, or the system secretly mixing integrated and dedicated GPU outputs.