Right click on the my computer icon, either on the desktop or in the start menu and select properties, then click on the hardware tab, and then the device manager button.
once you can see the device manager you should see an unknown device with a yellow exclamation mark next to it, double click on that and click on the details tab, select hardware ID from the dropdown menu and you should be a string of characters that starts something like pci\ven
Post that entire string and someone will look to see which driver you probably need.