USB-C won't recognise any external monitor.

[RK-NLS]

We have several HP EliteBook 840 G7s that have started to refuse to connect to external monitors via the USB-C ports - This functionality was working before December 2023 but has suddenly stopped working (The HDMI port still works).

Tested with fresh installs of both Windows 10 and Windows 11 using multiple display/adapter combinations plus HP docks (all confirmed as working before testing) and all drivers including dock drivers up to date no external monitor is being recognised via USB-C. 

Adapters tested: USB-C to HDMI, USB-C to VGA, USB-C to Displayport
Docks Tested: HP USB-C Dock G5, HP Thunderbolt Dock G5. 

Tested the available DP alt modes in the BIOS and reset BIOS to factory - Issue still present.

USB-C ports still recognise other devices including the docks, flash drives etc - Only display output affected.

[RK-NLS · Accepted solution]

Update: 

I made this post to help others; I've already fixed the issue: 

The issue is a fault with the latest BIOS (1.15.00) Released on December 5th 2023 - As we have multiple units of this model number I was able to test on a working unit - Unit connected fine to external displays; Update to BIOS 1.15.00 immediately stopped any connection to external monitors over USB-C. 

To solve the issue I got hold of a rollback BIOS version (1.14.00) and applied it - After several restarts (Windows asks for three restarts once you sign in) connections to External Displays immediately  worked again. 

I also noticed that you need to update all drivers and then apply the 1.14.00 BIOS (When applying the 1.14.00 BIOS on a unit that didn't have up to date drivers the functionality remained broken however updating all other drivers allowed the fix to be successful. 

Hopefully HP will release a fixed BIOS soon (we require up to date BIOS for security regulations and have 80 workers with this unit model who use them as their primary device connected to USB-C docks when they come into the offices).