No audio when connect HDMI to HDTV!!

I have a DELL inspiron 1526 laptop. It has SIGMATEL STAC 92XX C-Major HD Audio and ATI Radeon X1270 video with HDMI port. I installed windows XP SP2 on this machine with R171789 for SIGMATEL HD audio, the latest driver for ATI HDMI Audio Device (R2.03) and ATI Catalyst Control Center 8.9. When I connected this laptop to my HDTV (Samsung LN52A550) using 10 ft HDMI cable, no sound came from my TV. I can get video on my TV from PC. I can hear sound from laptop. When I go to the “Sounds and Audio Devices” at Control Panel, it only appears “SIGMATEL” in “Playback Device” menu, no ATI HDMI option. In “Hardware” under “Sounds and Audio Devices” and “Device Manager” I can see ATI HDMI Audio and it shows “working properly”. When I disabled ATI HDMI Audio from “Hardware” and tried to re-enable it, it shows “this device cannot start (code 10)”. If I boot up the laptop with my system connected to the HDTV, ATI HDMI Audio was not show up any more in “Hardware” under “Sounds and Audio Devices” and “Device Manager”. I tried to re-install Microsoft UAA patch and audio drivers for SIGMATEL and ATI HDMI Audio. The problem was still there. I’ve struggled with this issue for a week. Please help me if you have any ideas.