HDMI and Bravia XBR46 with Dell XPS16

I am having trouble connecting my HDTV with my Dell XPS16 through HDMI connections on both ends. I have had no problem connecting the HDMI from the laptop to a Samsung 32 inch HDTV through the HDMI cable so I know the cable is OK and that the connection to at least one HDTV works. I have tried connecting up to the Sony Bravia XBR6-46inch (with both TV on and laptop on), then switching TV to Output HDMI 2 (so output is correct). When I reboot the lapto the Dell Microsoft screen and startup appears on the Bravia TV and looks like it is going to work. Then when the laptop goes into the Vista 64 (SP2) bootup the TV screen goes back and there is no video/audio to the TV HDMI2. When I first bought my Dell XPS16 (running Vista Sp1) I checked the HDMI connection to the Sony Bravia XBR6-46 inch TV and both audio and video were detected. Is there something about Vista SP2 that is causing this problem with the Sony Bravia TV? It seems weird though that everything works fine with the Samsung 32 inch HDTV. Does anyone have any ideas what I can try, I have tried everything I can think of? Oh also I connected the Dell XPS 16 to a Panasonic Plasma HDTV (42 inch) and was able to watch my Netflix just fine, so it seems to be a problem only with the Sony and also only when Vista boots?