Hmmm... Lemme run through the things that I would try if I were there, in case any seem useful.

• Double-check all connections to make sure that cables are run to the correct ports on the 990 (including red, blue, and green for the three component connections) and that the connections are tight.
• Toggle between the two component inputs on the projector to be sure nothing's gotten turned around there.
• Try connecting a source to the Video5 input using either composite or s-video (I forget which is the default, so I'd try composite first and s-video if that didn't work). If the 990's switching is working properly and the projector is on the correct component input, you should get that video signal through the 990's monitor output.
• Hook a spare TV up to the composite monitor output of the 990 to get access to the menu OSD for troubleshooting purposes (so that you can properly configure the inputs you're using and start to eliminate - or identify - possible problems). Some people with projectors elect to pick up really cheap TV's for this sort of duty anyway, since it allows them to perform certain basic tasks without putting hours on their projector's bulb.
• Move the component cables from the 990's monitor output to the Denon's component output (again, as a way to help eliminate possible problems).

Obviously some of those would be last resorts, but those are the sorts of things I'd try if I were in your shoes.