two fx4500 in 1 box but no output

[scsjason]

I have a new box running fc5 (64bit) with two fx4500 cards but cannot
get them to work together. I have edited a config from a machine with 2
fx7800s in which does work and it will start X and gnome seems to
start up and connect happily to the display but the monitor is either
just black or puts itself into standby. If I drive the monitor from a
single card (in 2 large stripes) then it works, but driving it in 4 quads from 2 cards gives nothing. (Its an ibm T221 monitor). Also, with the lates drivers in the single card 2 stripe mode running openGL apps kills X but the previous drivers seem OK.

Any thoughts ?

[scsjason]

OK, more details: The machine has 8Gb of ram, if I strip it back to 2Gb
then all is well and I can drive the display (3840x2400) using four
outputs if 1920x1200, 2 from each card. When I put 4Gb back In
I'm back to the same position. I'm currently running memtest on 4Gb
but so far it shows nothing wrong.

Is there a meory issue with 2 fx4500 and 4Gb on a tyan thunder k8we
board ?

---------------
jason

[scsjason]

OK, fine with 2Gb, hangs on boot with 4Gb but memtest checks
out fine. Turning off the graphical boot loader seems to make it
work ok with 4Gb and then re-inserting all 8Gb and booting with
no graphical boot loader and it seems fine, even the latest drivers
seem to work OK too.

I seem to think we've seen trouble with the graphical boot
loader on dual card systems before. Still, at least its
working OK now, just need to try an get the synchronisation
sorted out . . .seem to get tears on the joins of 2 halfs
of one card and completely out of sync between the 2 cards and the
two halfs of the second card . . .