Cannot Startup From Alternate OS X Disks

I can only startup from the disk I have designated as the "Startup" disk in the "System Preferences." By that I mean, holding down the "Option" key during startup does not bring up the several disks with valid OSs on them that would normally show up, it just continues to startup from the designated disk. Likewise, if I hold down the "Shift" key during startup, it does not startup in "Safe" mode, it just starts up from the designated startup disk. Holding down the "c" key during startup will not startup the MacPro from my original "Mac OS X Install DVD." It will bypass that instruction and just startup from the designated "Startup" disk. This startup problem started about two weeks ago, but I cannot associate the change with anything I did.

I can only get it to startup from a different disk by designating a different disk in the "System Preferences Startup Disk", where all the l disks that don't show up with the "Option" key, do show up.

I have ONYX and Cocktail and may have inadvertently turned something on or off, but I don't think so.

Is there a preference file I can trash in the Library's Preferences folder that might cure the problem. Any suggestions would be appreciated.