Dell Precision 650 video card UPGRADE PROBLEMS

Upgrade Problem with video card PCI PNY Geforce 8400 GS 512MB on Dell precision 650 monitor goes black before entering bios set up and doesnt enters to windows XP, computer restart. Is this a Bios problem trying to recognized the PNY 512MB memory or this means incompatilibity?

My computer details
Dell Precision workstation
chipset Intel E7505
2 Xeon 2.4 Ghz CPUs
1 GB ram
AGP Nvidia Quadro FX 500/600 128MB
In Dell bios AGP is limited to 256MB

CONCLUSION

Above card its not compatible with dell precision  650worksation 100% sure. Im looking for a new AGP or PCI card of min 512MB- 1 GB that will be 100% totally compatible with this PC. Would be too much 512MB or 1 GB for this computer?

Any suggestions?