I had this same exact problem, except on the 27xt, which is the 27' version of the HP Envy TouchSmart. It's identical to the 23' only bigger. Intel Video Driver Update Windows 10 there. I called HP who told me to call Microsoft, who after an hour of Remote Desktop installing new graphics drivers and that not working told me to call HP. So, I googled the problem and found this thread, on this forum and I'm soooooo glad I did.
This document pertains to HP PCs with a High-Definition Multimedia Interface. More than one HDMI input. Next step to update your Windows drivers.
Pos58 Driver Windows 10. Hpuser30 is absolutely right, except I found an even easier method for fixing it. I went to my local BestBuy store, which sells the 23' version and I plugged a flash drive, I brought from home, into the USB 3.0 port on the side of the display.
Then I went to the c: drive and found their SWSETUP folder and I 'copied' the entire folder to my flash drive. Their machine works perfectly, in Windows 10, so I felt confident this could work. I went home and opened the SWSETUP folder on my computer and I searched for MyHPDisplayOSD and I found the folder named the same thing.
Inside that folder was a file called HP_My_Display_2.08.020_Setup.exe. I tried running the file but it said I couldn't, because I already had a newer version. Which was the problem in the first place.
Either Microsoft or HP had updated the driver to one that no longer recognize that HDMI port nor button. So I went to control panel and then programs and I uninstalled HP My Device, which required a reboot. Then, I installed the setup file on the Flash drive, that I got from the computer at BeatBuy. I didn't even have to reboot. I just pressed the HDMI IN button and it worked perfectly, the way it's supposed to. The store version is a 23' and mine is a 27'. The store version had Windows 10 Home and I have Windows 10 Pro, but the HP_My_Display_2.08.020_Setup.exe works on both.