It could be the graphics card, or possibly a short with the PCI slot.
I had a recent system with a Radeon HD2600 that would just go black randomly. Turned out to be a short on the card.
A few questions:
How long has this issue been going on?
Are you working with one or two monitors?
Are they Apple monitors?
1. If you’re working with one monitor, you can try plugging it into the second DVI port on the graphics card. If its happening on 2 simultaneously, skip to step 2.
2. Next I would move the graphics card to another PCI slot. See if the issue continues.
3. Finally if you have a second graphics card, try swapping out the X1900 and see if anything changes.
Also you may want to check the power supply on the monitor. Chances are it isn’t the cause, but you never know.
Let me know how it goes.
David Hall
Service Manager
Zero One Media Center
Apple Certified Hardware Technician