Users with older HP notebooks (e.g. HP ENVY 14) are flaring up in forums demanding graphics support for older notebooks. Many were complaining that the HDMI output no longer works as a dual display when connected to a TV (it worked on Windows 7).
Unfortunately official Radeon driver updates did not solve the issue as it did not support the old Mobility Radeon 5000 series (which includes dual graphics, Intel + ATI) which auto switches on power source for higher 3D performance.
The good news is that, you can now download the beta driver 15.11.1 from AMD website and everything should work fine just like it is on WIndows 7.
Do download at http://support.amd.com/en-us/kb-articles/Pages/latest-catalyst-windows-beta.aspx , install it and report back your experiences by commenting below.