That's how you start to troubleshoot such issues.
I suggest you post this in the PC help forum instead since it's likely more of an issue with Windows 7 and/or your software driver/video card settings.
I'm running windows 7. My computer does not detect my HMDI projector.
The projector works fine connected to a DVD player with the same HDMI cable and my LCD TV works fine connected to the computer as a 2nd display. Again, with the same HDMI cable. Hence, I don't believe the physical connection (HDMI port/HDMI cable) is source of the problem.
The computer simply will not detect the projector as a display device....
I'm totally baffled. Please help.