2006 Mac Pro + NEC 3090 - grey screen not displayed during boot

Question

I have a September '06 Mac Pro 1,1 (Woodcrest variant) hooked up to an NEC 3090 30" LCD monitor, running OS X 10.5.7. Previously, I was using an Eizo S2110W 21" LCD; turning the monitor and computer on would cause the following to be displayed (in order):
1. Light grey background with dark grey Apple logo with spinning thing.
2. Solid blue background.
3. Leopard wallpaper.
4. Log-in dialogue.
Since using the NEC, the grey screen is not displayed at all: the display stays blank until the blue screen is displayed, and then the Leopard wallpaper and so on. This is using the 2560x1600 native resolution of the display, and has occurred using both 10.5.6 and 10.5.7.
If I change the resolution to 1280x960 and boot, the grey screen is displayed. If I change it to 1600x1200, I get weird corruption on-screen during the period when the grey screen should be displayed; for some reason, this includes part of the desktop wallpaper I was using before I rebooted.
Resetting the non-volatile RAM using Command-Option-P-R works for the very first time I boot the computer, though the grey screen is displayed at very low resolution. If I reboot from the log-in dialogue immediately afterwards, normal behaviour occurs - i.e. the blank screen.
The upshot of all of the above is that if I want to boot into Windows, or install OS X (e.g. when Snow Leopard comes out), I have to remember to boot into my existing OS X installation, change resolution, reboot whilst remembering also to hold down the ALT/Option key. It would be much easier if I could do away with having to change resolution.
I have tried connecting the monitor to a PPC Mac mini at 1600x1200 (it won't go any higher), using Tiger 10.4.11 (not sure of exact version - the latest). At this resolution, the grey screen is displayed.
Using a '08 MacBook Air (first generation) and the supplied DVI adapter, also at 1600x1200, nothing is displayed on the NEC until I get to the log-in screen. This occurs if the NEC is set to be the primary display or the secondary one - the only difference is where the log-in dialogue is displayed. I am not familiar with dual-screen behaviour, so I can't say whether anything is supposed to be displayed or not (i.e. does the grey appear on both displays?).
I have been in touch with NEC Europe support on this issue, who suggested it might have something to do with the 10.5.7 release. I know this not to be the case, as it was occurring prior to 10.5.7 being released.
Any ideas?

Answer 1

Put more of your hardware listed in your profile.
I looked and don't see you list your graphics card anywhere.
Graphic card it came with was either X1900 (watch for heat and dust bunnies and clogged vent);
OEM 7300GT (seems unlikely).
You could have replaced either with 8800GT or ATI 3870.
Require 10.5.2+ ideally 10.5.6+.
Some problems cropped up with 10.5.7. 10.5.7 doesn't work on some (many) 3rd party displays and stay with 10.5.6 if necessary until it is fixed or resolved.
But you say it happens with 10.5.6 also, and was doing so before 10.5.7? which makes your problem somewhat different or unique.
Zapping PRAM or NVRAM reset obviously shouldn't be needed repeatedly. And your graphics card probably needs to be replaced, or test with another card to rule it out.