I have recently got a HP xw9300 workstation. Its default GPU was a Nvidia Quadro FX3450. I swapped in a newer Radeon 5450 because the older GPU didn't suit my needs.

Now, the problem is that the new GPU is not working as it should. Gnome Shell won't start. It would hang to a screen showing only the desktop. Glxgears run with vblank_mode=0 show a drastical drop in performance. Almost 50% less than when I used the same GPU on my Pentium D computer.

Looking at startup lines, there are some errors related to "Powernode-k8", seemingly not related to this problem. There's also a Firmware error regarding a "PCI device" and "ACPI".

I already installed the "firmware-linux-nonfree" package".

What could possibly be causing this?

Thanks in advance.

Which driver are you using? The open source radeon driver or the proprietary fglrx driver?

Can you show us your /var/log/Xorg.0.log file?

Adam