|Matrox G450x4 MMS|
See the User Guide - there's lots of troubleshooting info in it.
"Maximum resolutions (per display)
Digital: 1280 x 1024
Analog: 2048 x 1536"
If you are using LCD, or LED LCD, monitor(s) are you able to set each monitor's resolution to it's "native" or "optimal" resolution ?
Apparently it's a PCI card.
HP Z400 Workstation - Specifications and Warranty
NVIDIA Quadro NVS 295 (256 MB); NVIDIA Quadro NVS 450 (512 MB); NVIDIA NVS 300 (512 MB); AMD FirePro 2270 (512 MB)
NVIDIA Quadro FX380 (256 MB); NVIDIA Quadro FX580 (512 MB); NVIDIA Quadro 600 (1 GB); ATI FirePro V3800 (512 MB); ATI FirePro V4800 (512 MB); NVIDIA Quadro 400 (512 GB)
NVIDIA Quadro FX1800 (768 MB); ATI FirePro V5800 (1 GB); NVIDIA Quadro 2000 (1 GB)
NVIDIA Quadro FX3800 (1 GB); NVIDIA Quadro FX4800 (1.5 GB); NVIDIA Quadro 4000 (2 GB); NVIDIA Quadro 5000 (2.5 GB); Elemental Accelerator Software for NVIDIA Quadro
2 PCIe Gen2 x16
1 PCIe Gen2 x8 mechanical (x4 electrical)
1 PCIe Gen1 x8 mechanical (x4 electrical)
2 PCI (full-height/length)
1 22-in-1 Media Card Reader (optional)
(The PCIe x8 connectors are open ended, allowing a PCIe x16 card to be seated in the slot.)
Apparently you have two PCI slots on the computer.
The PCI slot closest to the center of the mboard usually shares it's IRQ with the video adapter, when there already is a video adapter present.
If you have any PCI card other than a PCI video card installed in that slot, you are likely to have problems.
If you DO have a PCI card installed in that slot that is NOT the Matrox card, try installing the Matrox card in that slot, the other card in the other PCI slot.
If you DO NOT have a PCI card installed in another slot, try installing the Matrox card in the other PCI slot.
Installing a PCI video card DOES NOT automatically cause the bios to disable any other video card installed in a slot, or the onboard video if that applies.
If you want the Matrox card to be the primary card in Windows, you must set Initialize video first or Primary video or similar in the bios Setup to PCI, Save bios settings.
If you do not want to use the other video adapter, try Disabling it in Device Manager - Display adapters by RIGHT clicking on it.