Just downgrade your bios firmware to 1.09 and it will work.
The problem is the new firmware 1.10, which does a check on hdmi activity on cold boot and deactivates gfx.. Got 2 mainboard replaced before i tried the downgrade.. wasted a good deal of time on this..
If you have problems finding the older bios version, then look for 010009-Windows.exe on the dell ftp site..
Update --> great job by Intel & Dell in getting the problem resolved with latest BIOS & drivers. If you have HDMI issues with Panasonic,
please use latest BIOS 1.1.0 from Dell site & latest Windows7 drivers 32 bit from Intel site or dell site. Works like a champ now - Andi