To run through all the scenarios, look at the image below and we'll go from left to right...

• Component: You can connect this output to the HDTV, but if the HDTV can't accept 480i on the component input then you will not see the 990's menu, transcoded composite video inputs, transcoded s-video inputs, or any 480i component video sources. Therefore, if you make this connection, set the HDTV to the appropriate component input, switch the 990 to a video input (DVD or Video1 through Video5), and don't get an onscreen menu when you press the MENU button to the right of the zero on the 990's remote, we should move on to our other two options...
• Composite: You can connect the composite monitor output to a composite video input on the display, but you will only get the onscreen menu and any composite or s-video inputs through this connection. If the component didn't work, you can try this one to see if there's an issue with 480i to your TV's component input. Make the connection (from the marked monitor output in the middle of the picture above to a composite input in the TV), switch the TV to that input, switch the 990 to a video input (let's use Video5 just to get one that should be clear of any higher video connections), and press the MENU button next to zero on the remote. Two things should have happened. First, the 990 should have popped up a little message when you changed inputs to Video5 (assuming you haven't disabled OSD on that input) saying "Video5" and a few other things. Second, the MENU command should pull up the on-screen menu.
• S-Video: For what we're doing, s-video and composite are going to be treated exactly the same way - and if one works, so should the other.

Cvinfig makes a good point at the end of his post. You need to make sure the TV is set up to actually use the inputs you are connecting to - if you've disabled the composite or s-video so you don't have to skip through them when changing inputs, you would need to re-enable them for this test at least.