can't make ibook play through TV

[drharrietd]

Please can someone help an absolute dummy? I have an ibook and a Hitachi HD TV. Last year I bought a cable -- can't remember what it's called but it is the right one to connect the ibook to the TV. And last year I connected it up and it worked fine -- no sound, just picture, but that was what I expected.
I then didn't use the system for a year. Now I want to start using it again and I can't make it work. These are the possible reasons:
1) I've connected the cable to the wrong place on the back of the TV -- but there are only 2 sockets on there where the cable will go and I've tried them both without success.
2) I don't know what input setting to put onto the TV. I can choose between ATV, DTV, AV1, 2 and 3, and Component. I've tried them all and none of them work.
3) There's something I'm supposed to be doing on the ibook to make it play through the TV -- this seems likely but I can't remember or find out what it is. There's a little icon of a TV set at the top right hand side of the screen with a drop down menu which reads "Detect Displays" and "Turn off Mirroring" -- then it has settings for FPD TV and Color LCD. It's picked these automatically.
This is driving me crazy. If you can help I will be very very happy. But please keep your answer as UN-technical as possible as I am not a technical person.
Many thanks in advance.
Harriet