Sorry if this is a little long; I'm trying to be precise.
I have an Intel i7-4770 desktop PC with an Intel HD 4600 graphics card. After 3 months a disk drive failure forced me to reformat the system partition and install Windows 10 from scratch. Something went wrong with the Windows installation, so it was not using the HD 4600, just a Microsoft generic PnP monitor. From intel.com, I downloaded and installed driver win64_15.40.5171.exe. I confirmed it is installed using DxDiag.
My main monitor is a 1080p Lenovo LT2323Z on DisplayPort 1, and I use a Samsung 1080p HDTV as a second monitor on DisplayPort 2. When I first set up the new PC, the HD4600 was installed and configured and for 3 months I was able to use the HDTV as a second display. Now after the Windows re-install and manually installing the HD 4600 driver, the LT2323Z works properly and I am able to use the Intel Graphics app, but the HDTV doesn't get anything from the PC. When I connect the HDTV to DisplayPort 2, my main monitor goes blank (as though it had switched to Display 2), but there is still nothing going to the HDTV. The only way to get my Windows desktop back is to physically disconnect the HDTV.
I tried reinstalling the win64_15.40.5171.exe driver and rebooted, but nothing has changed.
What must I do?