welcome to the forum, and firstly dont apologies im english and i understood you
I think the standard windows loading resolution is 800x600, as thats the default resolution when you dont have video drivers.
I think youve already guessed the problem, your tv doesnt support the native resolution.
im not sure but you could always try updating your video drivers, or having a play in the catalyst control center.
as it has a section for HD TVs,