Thanks for everyone's input. The issue got solved to some extent. However, more issues appeared...Here is what happened.
Step 1>. Since D-SUB works fine, I powered on the computer with ONLY D-SUB connected to a Dell monitor. After the Windows 7 was loaded, I then plugged in the HDMI cable and connected it to my Toshiba HD TV. Suddenly I got signal through the HDMI and I could change dual monitor settings without any issue. I ReStarted the computer a few times, no issue either.
Step2>. However, weird things happened when I shut down the computer completely. All the settings seemed lost… I still had D-SUB connected to a Dell monitor and HDMI connected to Toshiba HDTV when computer was off. And then I powered it back on. Suddenly I lost the HDMI signal again! The weirdest part is that when Windows 7 was loaded I tried to unplug and replug in the HDMI, windows 7 didn't detect my Toshiba TV at all. With D-SUB and HDMI connected at the same time, I rebooted, powered off&on many times, still no signal through the HDMI.
Step3>.In the end, I unplugged the HDMI completely, leaving only the D-SUB connected; powered off completely and on again, basically repeated the step 1…When Windows 7 was loaded, I plugged in the HDMI. Suddenly, Toshiba HDTV was detected again…
I have updated the Bios firmware as well as the VGA driver. I also set the Bios to enable multiple monitors. However, the issue still exists: I have to shut down the computer completely -> turn it on with ONLY D-SUB connected -> plug in HDMI when Win 7 is running. Every time I shut down the computer, I have to repeat the process to get HDMI working…This is annoying. Is there anyway that I can just start my computer with ONLY HDMI? Or did I really get a bad board???
Thanks!