And difference from that workstation and to the others i have in the offices, is the 2 monitors aren't the exact same model.
i only have that disabled problem with the station with 2 diff model monitor. ( but still the same brand and line of product. )
Check and make sure the video cable is securely attached to the video card. Maybe a loose plug making the monitor go on and off, or the power cable also. Try a different DVI to vga adaptor if you are using one. Always check the easy things first.