There are sever things that COULD cause this, but try the following:
-Update your directX to the newest version
-Update your video drivers
-Be sure you are in a game level when using console (Console does not work at the menu screens)
-Change screen resolution (Both for your game and perhaps for your desktop too)
-Use a mod like Age of Redemption mod:
http://www.e-mods.net/downloads/mods/AoRSetup_4_23_2006.zip (Try both with and without CD shortcuts)
I noticed that console sometimes doesn't pop up for me as well. This only started happening after I bought my
widescreen lcd monitor.