Also, the OP has to be informed that not all 8600GT cards are HDCP-compliant. Many of them are not, unfortunately, despite the claims from the makers of the cards. I tested a friend's system with a very similar video card, with the exact same version of the software. In that particular case, the video card failed the HDCP compliance test. The monitor could not be tested (and thus its HDCP compliance grade was listed as "NA" or something similar) because the video card failed the test. And even with the very latest version of the player software, the video board still failed the HDCP test. And when I tried playing a Blu-Ray disc on that machine with the monitor reconnected through DVI-D, I got only a blank screen - no video output at all. In that rig, the only way to get things back to "normal" after this failure to display an image was to restart the entire system since none of the keys on the keyboard would even function. No wonder why the owner of that rig had to use the analog VGA connection so that he could play his Blu-Ray discs on that machine (albeit at a reduced, 480p resolution that's been downsized from 1080 lines using a bad resizing alogarithm).
If on the other hand both your video board and your monitor are from a reputable company, and both claim to be HDCP compliant, then you may need to update your Blu-Ray player software in order for video to be output from hi-def discs via the DVI or HDMI out.