Graphics card problems

I have installed a Sapphire Radeon HD 3850 AGP card and have nothing but problems with it. My machine is a single core P4 with an Asus P4V8X-X motherboard, which uses VIA chipsets.
I upgraded my PSU to a Corsair VX 550W and have 1.5GB of RAM.
The card just will not perform. In SMARTGART the AGP speed is Off, and any attempt to switch it to 4x or 8x results in it switching to Off again when I reboot.
Anything but the simplest games are unplayable, the PC just crashes.
I read that AGP speed constantly switching to Off is a common symptom of bad or missing chipset drivers so I tried to reinstall the drivers using my motherboard installation CD.
All I get is a message saying that it cannot find the setup.Exe path, or one of it`s components, and says "check path and filename are correct and that all required libraries are available".
I don`t know whether I could download chipset drivers direct from the VIA website, or whether they still supply the drivers for this 5 year old machine.
Any advice please .

You`ll find the MB drivers here;

http://www.driverstock.com/ASUS-P4 [...] index.html

Read the page carefully, or you could instal the wrong ones.
As usual; Unilstall the existing drivers first, then restart, then install the new ones.
Also, check the website of your card for updated drivers, there have been driver related issues with AGP HD3850 cards and it is possible your card came with older drivers.
As far as I know, the AGP 3850 is not supported by ATI so do not use the drivers found on their website.