HDMI fails to recognise new monitor

[greenelephant]

Windows 11

VGA monitor works fine

Connecting via HDMI to Lenovo Legion R25f-30 monitor fails - screen goes into standby, the monitor's menu is disrupted. The VGA screen becomes unstable, resizing the windows & then resets itself. The mouse still works.

Tested the HDMI output by conenction to an old TV - no problem. Win 11 detects it & extends or duplicates the image.

The monitor works when fed a video signal from a recorder. Its menu appears ok.

Windows System/Display tools fail detect the new monitor, irrespective of whether the VGA monitor is connected.

Device Manager shows :

Display Adapters/ intel UHD graphics 730, with up to date driver

Monitors / Generic Monitor (SMS22A100) (which is the VGA device)

                          It also shows the new monitor when it is connected, again claiming to have up to date driver

Lenovo Accessories and Display Manager can detect the device.

PC is HDMI 1.4, Monitor HDMI 2.1, as I understand it this should work, just at the 1.4 standard.

So, it looks as if Win 11 is doing only half a job. Ideas please.

[greenelephant · Accepted solution]

Hmm, this has been interesting. Basically I was using cables that were too good, i.e. fit for HDMI 2.1, but as I was using 1.4 as the source I needed an old (slow) cable, & of the 3 HDMI cables in the house it was the one I had not tried. 

Not what I was expecting from reading about 2.1 being backward compatible, but not clear that the cables weren't.