probably something to do with having the 2nd output connected 'activates' an automatic function that sends an 'average' safe signal to the 2nd monitor.
that might be specific to the 2nd output or it may be when there is a connection of both connectors that creates a circuit.
go here and input the information and use something like 'second monitor' in the search pane.
obviously if the graphics card isnt setting itself up to work with the hdtv on the first try.. there is no 'automatic' going on and that could be seen as a limitation.
you havent messed with the driver controls yet?
thats generally where the magic happens.
i dont have any experience with ati drivers.. so i cant just briefly remember what you need to do.
i'm guessing you need to select the appropriate output method and press apply.
if your computer monitor doesnt support the same resolution/method.. you might lose all video output to the pc monitor.. but plugging in the hdtv should work if you plug it in.
'auto' should be the default in the drivers.
makes me think something else was selected manually.
there are plenty of articles available.
youtube also offers video tutorials.. such as this:
http/www.youtube.com/watch?v=PsSUeVfS71Y
help yourself begin.. and tell us you have tried and what step you got stuck on.
its upsetting that you cant figure it out just by looking at the driver control panel.
the only way i am going to continue helping is if you go into details about what you have done and what is missing.
from your original post.. it looks like you have hooked up your hdtv to the main connection and it didnt work.
then you hooked up the pc monitor to the first connection and the hdtv to the second connection and they both worked (the graphic cards 'auto' function)
if you havent done anything more, the driver control panel is where you need to be.
IF the driver control panel wont do what you want, try different drivers.
its a standard that every setting has a pop-out window or something at the bottom to go into detail about what each setting does.