need help asap on having Radeon 9000 pro put in my cube! :(

[musik54 at comcast.net]

I would love to get some help asap!  :(  I have a 450 cube which is stock, except for added RAM and the HD has been upgraded.  I took it to a mac store last week, so that he could upgrade the video card, so that I would be able to use it with the new 23" apple hd cinema display, which I just got via a fantastic deal.

At any rate, the guy at the mac store says that after putting in the new video card, he can't get the cube to drive ANY monitor at all.  If he takes out the new card and puts it back to stock, then I won't be able to use the new monitor.  I've checked cube-owner.com, and if I'm understanding things correctly, I believe this combination is possible.  This guy has a retail store specializing in apple prodcuts and he personally has an upgraded cube of his own (with a higher end card), which he did himself, and he has a good reputation here, so I don't suspect his work.  He says he has taken apart all the components possible and tried them in other settings, and each individual thing it could possible be has no problem working in another situation, only when it is all together inside my cube and trying to drive a monitor.

Help!  Does anyone have any suggestions? He's of course willing to give me my cube back the way it was at no cost, but that leaves me not able to use my new monitor (since, as I understand it, the stock graphics card in the cube won't drive the new 23" hd cinema display, only the old 22" one), when I'm pretty sure that I should be able to use it.  :( 

FWIW, the firmware upgrade was done, and I'm using panther, which worked fine with my old CRT, and everything on the cube is in working order otherwise.

All hints/suggestions appreciated!

Martha in California