I had intermittent detection of the HDMI in "Control Panel/Sound", and eventually no detection (the following solution may also work for those who were never able to obtain a signal at all). For me updating the audio driver fixed the problem. You can update the audio and video drivers by following the steps below (found these steps at Microsoft website). My computer is only 6 months old, but still needed the drivers updated. No special system setting are required as written in previous posts, if the driver is the problem. I was also extremely frustrated with the ongoing problem and hope the driver updates work for you. Good luck!
- Open Device Manager by clicking the Start button , clicking Control Panel, clicking System and Maintenance, and then clicking Device Manager.* If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
- In Device Manager, locate the device you want to update, and then double-click the device name.
- Click sound video and gaming controller
- Open each audio controller in sound video and gaming (one at a time) and update by Clicking the Driver tab, and then click Update Driver and follow the instructions.