Unfortunately, HDMI is (to quote a phrase) : 'a bag of hurt'.
Part of the problem is the HDMI/HDCP spec and handshaking and part of it is Windows making a hash of detecting the handshaking. There are many threads on Avforums and Avsforum with many HDMI issues and kludges to overcome them. Some things that may help:
Update your Receiver firmware. I was having issues with losing audio by turning the TV off and a firmware update in the amp cured it (they decoupled the input and output EDID).
Delete/disable any windows audio devices that you don't use. The only windows output audio device that I have enabled is the HDMI (NVIDIA in my case) so that when HDMI comes and goes it is the only thing available to windows.
You may get help from little programs that keep the HDMI active or 'restart' it when it isn't. I think one is called HDMIon.exe. I haven't tried any of these, but heard of several.
Try to redetect displays with 'windows key + P' and 'enter'. You shouldn't have to reboot to get it back. Some have programmed a macro on their remote to do this!
Finally, one almost guaranteed solution is the Gefen HDMI Detective. It's quite pricey for what it is, but it is a kittle black box that keeps your PC thinking that the HDMI info hasn't changed and stops any handshaking.
Hope this helps!
SBR