I've had this problem with my ps3 which uses an HDMI cable. As you know HDMI uses HDCP which is basically DRM for HD. If the encryption is broken it will block the audio and video.
To fix this encryption so far i found that turning off your tv and back on will renew the key and fix the encryption allowing the signal to pass thru. That's my theory though as so far that has worked 100% of the time when all I get is a black screen.
In power options ,win 7, there is a pci-express power saving option, link state power management. Its set on , on the balanced plan. Believe its off , on the high perf. profile. You might want to check that. Might play with the connection.