ATI 5xxx series have ,depending on the VGA BIOS used ,issues with some PCI 1.x motherboards and if i am not mistaking that nvidia chipset on the motherboard is not PCI-E 2.0 compatible ,what the video card BIOS may be expecting.Issues were observed with the first batch of ATI 57xx seres though.
A proper VGA BIOS should fix this if the card is healthy.
Get that video card VGA BIOS updated with latest BIOS version available ,on another working system ,and if this doesn t help then upgrade the motherboard.The power supply seems to be beefy enough.
I would call/e-mail HIS support about this.