1. Try the video setting in the BIOS in all modes it offers.
2. Remember that the motherboard drivers must be proper before a video card will be identified proper. This derails a few that thought they only needed the video card driver.
The power supply looks small for what you've listed. I wouldn't be surprised if it's either the issue or will be a future issue.
I am working on a HP a815n desktop, with a P4 3.06GHz processor, RAM 1.5GB, PSU 300W, onboard video 82915gl integrated graphics. I am trying to install a pci ge force 5200 fx. I am now on day 2 of trying to figure this out. I have tried using Driver Cleaner Pro, uninstalling everything in display. All drivers are current for the computer. Tried using the nvidia 84.21 driver. And still no luck. When everything is uninstalled and rebooted, change in BIOS video PCI, all I get is a blank screen and the monitor says it is going to sleep. HELP!!!!! I am at wits ends.