I just got my xbox 4 weeks ago, and everything has been working fine since I got it. I have a Sony bravia 40" 1080p 60Hz HDTV. my xbox is connected to my TV through an HDMI cable and an HDMI audio adapter.
I turned my xbox on today. usually it takes maybe 2 seconds for my TV to recognize the signal coming from my Xbox and show the xbox start logo, but this time it took a good 20 seconds. when it finally did show up, the picture was 640x480, in a letterbox, much less than the normal 1080p i usually get out of it. I also noticed there was no sound. I went into the system settings and changed the picture back to 1920x1080. I then went into the audio options and tried turning it to digital stereo and then to the third option (I forget what its called) but no luck. I tried connecting my xbox to the TV through a different HDMI port, using a different HDMI cable altogether and then without the HDMI audio adapter, but still no sound. The picture, which I changed to 1920x1080, is still the same, though, but i don't actually think that its true 1080p, because usually it will say on the top of my TV in an info bar when I switch inputs something like "1920x1080, 1080p" and now it only says "1920x1080, 60Hz".
I really dont know where to go from here. this is really strange because I cant remember any changes I have made to my setup or options that have caused this, it just seems to have come out of the blue.
Can anyone give me some advice on how to proceed next? I would really appreciate it.