Hi Terryd68, welcome to BC.
There are a couple things you will need to check.
1. Your television may need to be programmed if you have more then one input setup, exactly like you would if you were hooking up a DVD player or VCR. Check your televisions documentation.
2. Check your video settings in your computer. The TV should show as a second monitor or at least be available for selection from the monitor type drop-down list. You will also need to lower your resolution settings while using a tv for display.
Without knowing what TV and computer make and model you are using, I can't get anymore specific.
Post that info back when you get time.