I hate when my electronics play hide and seek, then one of them finds a good spot and next thing you know the computer is crying and quits playing.
You need to give more info for any type of trouble-shooting.
How are you connecting them, what did you try already aside from plugging them in. Did you select the proper input on the TV? Is this a laptop or a desktop? If it's a laptop, did you enable output to the second monitor (usually it's a function key plus F5 or something)? Is this a seconadary monitor or your primary one?
Take a look at this guide to make sure you aren't missing any steps. Here is how to hook up your Vista laptop to your TV.
1. Locate and note the video output ports on the laptop. Video ports might be located on the sides or back of the computer.
2. Locate and note the video inputs on the TV.
3. Select a video interface cable that is compatible with the ports the two devices have in common. For instance, if the laptop has HDMI output and the TV has HDMI input ports, you can connect them with an HDMI cable.
4. Plug one end of the video cable into the video port on the laptop and plug the other end into the video input on the TV.
5. Turn on the TV and change the source channel to the appropriate video input. You might have to press a "Source," "Input" or similar button on your TV remote to select the channel.
6. Click "Start," type "Windows Mobility Center" into the search box and click "Windows Mobility Center,"
7. Click "Connect Display," select one of the display options in the list and then click "OK."