My thought here is to make sure that the analog video switching is working at all. With your cable box and DVD player being your only sources and with both being DVI/HDMI, you aren't currently using any analog video switching.

Here's the process that occurs to me. Connect either the component or composite monitor output of the 990 to an input on the TV and switch to that input on the TV. Connect a composite video source to the 990 (a cheap VCR hooked up to the front panel would suffice, or even a video camera or digital still camera with a video output - just something that will create a video signal) and switch to that input on the 990. Actually, I'd probably recommend using composite video to the front input because I'm pretty sure the default configuration for that input is the composite input. Then see if you are getting video from the source to the TV. If you don't get anything, you might even try resetting the 990 in case the default video connection used by that input of the 990 was changed - a reset would change the Video5 input back to a default of "composite."

Another test would be to try connecting the composite video monitor output to a different (small would suffice here) TV to see if you can get the menu that way. I doubt that the problem lies there based on what you've done to now and the results you've seen, but while I'm tossing out ideas I may as well toss them all out.

Troubleshooting this stuff can be hugely frustrating, but one way or another Outlaw and the gunslingers around here can get you back in business.