It may be that you can only display typical TV resolutions.
and several resolutions lower.
I heard that when you use HDMI you can't go beyond 1920X1080. BUT.. your TV may not have the ability to display that resolution so it may not be selectable. Also, make sure you have your tv on BEFORE you turn your computer on.
Going from HDMI to VGA is kindof odd... Is the VGA going into your TV or is it the HDMI that is plugged into your TV and which end is plugged into the computer?
It goes HDMI from the tv to the pc's VGA input on my graphics card... I am currently using a custom resolution atm. My monitor (tv) DOES pick up the other resolutions but displays in very poor quality, and you can see the screen "fluttering" when selected. My computer does pick up basic 1024x768 but it basicly makes having a big montior pointless..... But the catch is - in video games i CAN use higher resolutions, just not on my desktop and programs