Running four monitors after about 5 mins 2 monitors go off, been running this setup for almost a year never had this problem. 08 Mac pro. Osx el captain

ati radeon hd 2600 xd (the one cutting out)
and
amd radeon hd 7950


SKIP TO 2:50!!

 

08 Mac Pro???? Jesus... Dude Im not trying to be a dick, but unless you're trading Forex or a serious flight sim gamer. Give your graphics card a rest. 2 should be plenty for audio production.

 

running slaves

 

did you touch anything on the hardware side lately?
OS updates?

i would start by disconnecting every monitor cable after login, then reconnect them starting with the 2 on the 7950
unplug the cable from the cards, not on the monitor side

if no success, shutdown, disconnect every monitor except 1 on the 7950, then after login reconnect everything

if no success, same procedure again
but remove hd 2600 first, pram/smc reset, after login reconnect second monitor and shutdown, insert hd 2600, boot, after login reconnect the rest.

while connecting, always give your machine 3/5 sec in between

at this point if still no results its time to take a look at your hd 2600's health status,
dust/thermal paste, but first try another GPU if possible.

 

thanks for the reply after doing about everytest and trouble shooting method i could think of i just tried swapping out pci slots the after switching 3 times the last one worked and no issues since running smoothly thus far