If you have two monitors connected directly to your computer on seperate video ports, then they are both active at the same time.
If you have a splitter or switchbox setup so that one video port feeds two monitors, then the instructions that came with the extra equipment should tell you what the process is for switching between monitors.
If you are set up to do the much more common 2 computers sharing the same monitor then the key to press is typically the scrolllock key twice rapidly.
Right-click on an empyt area of your Desktop and select Properties from the pop-up menu. Select the Settings tab.
On this Window you can configure the layout of your multiple monitors.
You will see two monitor diagrams in your window, labelled 1 and 2. Typically number 2 is located on the righthand side of number 1, but you can drag its position around.
Click on the number 2 monitor and make sure the checkbox box located near the bottom of your windows called: Extend on Desktop onto this Monitor is checked.
Then if you apply and click OK, you should now be back to your Desktop. Move your mouse pointer off the righthand side of your computer monitor. It should appear on your LCD T.V.
If it does, then you are all set to use both monitors at the same time. Simply open an app like a DVD Movie Player and then drag it off the screen to the TV and drop it just like you would when moving any Window around.
If you want the TV to be the primary video display you can set this in Display Settings as well.
I know this doesn't answer your Hot Key question exactly, but I don't think desktop computer multiple monitor displays have the hotkey function that laptops do, where you would hold down the Function Key (Fn) and press the F5 key to switch active ports (the key on some laptops may vary but almost always have an icon of a laptop and a rectangular box side by side.
<grin> Come to think of it, I didn't ask you if your computer was indeed a laptop. This would mean that I took the long way around answering your question!!!!!