I connected my Acer's Aspire-5745 HDMI Cable to my Panosonic HDTV for an Extended Display and the laptop detected the TV and I was able to extend the display. No problem, just select HDMI-2 on the TV screen option whenever I wished to extend the laptop's display. After a time, this no longer worked. Now, if I wish to extend the display I need to do a System Restore to a time when the display extention worked for the laptop lno longer detects the HDTV.
I've tried through the Screen Resolution, Window Icon + P, the Intel Graphics and Media Control Psnl and more.... Only System Restore to a safe date will work.
If you have another display output option, like vga, boot up with that connection, if that works ok shutdown and reconnect the tv using the hdmi and boot back up. This happens to my htpc once or twice a year and just changing the connection fixes it everytime. Samsung TV by the way.