Since your laptop comes with switchable graphics then the generic graphics driver we have in our website will not work fine. The laptop manufacturer creates a special graphics driver for switchable graphics. I recommend reinstalling the graphics driver they provide. You can use this link http://h20000.www2.hp.com/bizsupport/TechSupport/ProductList.jsp?lang=en&cc=us&taskId=135&prodTypeId=321957&prodSeriesId=5296234
As an additional troubleshooting step I recommend testing the HDMI port with each graphics card to see if the issue happens with both graphics cards or not.
I have the same problem, it wasn`t present in Windows8 RC version when Intel finnaly decided to make proper driver support for Core i3 1st gen also. Switching to Windows 8 64 bit brought me to the same problem , the only "fix" till now is to make the TV or whatever you have conected to your HDMI port as Extended Screen, this way i get image on HDMI also, leaving it to Clone only or Single Display over HDMI just sends blank image over it.