Apple Cinema Displays make OSX crash - or not

Question

Hello everyone, I am new to these forums, though I have often checked for answers here.
I have looked as best I could for issues similar to ours but haven't found any yet, so here it goes:
Our system:
System Version: Mac OS X 10.4.11 (8S2167)
Our two Apple Cinema Displays:
Displays:
Cinema:
Display Type: LCD
Resolution: 1680 x 1050
Depth: 32-bit Color
Core Image: Hardware Accelerated
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Rotation: Supported
Cinema:
Display Type: LCD
Resolution: 1680 x 1050
Depth: 32-bit Color
Core Image: Hardware Accelerated
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Rotation: Supported
Never had a problem (Computer purchased in mid-2007). However, a couple of weeks ago, it started: the OS wouldn't start. After a few trials and tests and wonderments, we realised that what prevented it from starting (you know, whirly thing then sometimes apple logo then just light blue: frozen) was the way the screens were plugged into the computer.
At the back of the computer there are four connections for the displays, two at the top and two at the bottom. They used to be connected to the two bottom ones. Then we realised that only attaching one single display to the top right connection would allow the computer to start.
Further tests led us to attach the second display AFTER the whole OS was up and operating, again at the top (next to the only functioning one for startup), and the displays work perfectly. However, if I leave them in this arrangement and turn off the computer, when I start it again the system crashes, like before.
I am pretty sure at this point that a hardware problem is causing a software crash, but what do you think it consists of? We performed all the tests, including the extended hardware test with the installation disk. No problems were found at all.
Would it be helpful (or harmful!) to take out the graphics cards and place them in different slots?
Thanks so much in advance,
Valentina

Answer 1

Hi, I have tried shifting them around, and the problem does seem to follow the graphics card, despite all tests indicating they are both working properly. Any other arrangements will cause a grey screen to come down while starting up and say I need to restart the computer.
Changing the slots for the graphic cards, but keeping the display attached in the right place, would allow the computer to turn on but a window would come up saying that they weren't optimally configured (16x or 8x or 4x speeds). The best configuration remains the one I begun with (slots 1 and 4). The computer will only start properly with the display in slot 4, right hand side looking at the back of the display, and only when it's turned on will it allow me to attach the second monitor, again, only in slot 4, to the left side.
The same would work if the card was in slot 1, but it would tell me they weren't configured ideally so I put the card back in slot 4.
At this point, then (I have also just tried resetting the PRAM by pressing cmdoption+PR when restarting, but no changes) should I reconfigure the graphics card? (If yes, how do I do it?)
Thanks again, Valentina