have you gone into a custom setup by accident?
If all else fails you can reset back to default by removeing BOTH batteries (small power cell hidden near the main battery I think.
Just another thought . have you put the top dial into an auto mode or a picture style
That changes the menue vastly on my 350d
I know its the case on my 350 that in the picture styles it only allows jpeg so you cant select RAW and all the paramaters are dissabled as they are set by the style.
At least it was something simple (not the operator ) its very easy to knock things into the normally unused.
I had a similar problem on a shoot... the focus points and some display items disappeared on the top display of my 40D. I switched to a different camera and kept shooting -- later I noticed that I accidentally turned off auto focus.