|It would help to list the motherboard model number correctly. Could it be GA-8i915? And there's more to the number than that. Gigabyte has dozens of boards based on different variations of the i915 chipset. For example, these 4 boards are based on the i915GV:|
And these 3 are based on the i915GL:
And there are several others: http://www.gigabyte.com/products/li...
The power supply specs (make/model, wattage & amperage ratings) should be on a label on the side of the PSU. You'll have to open the case to get a look at it. Post back with your findings.
This article will help you to choose a card: Best Graphics Cards For The Money: May 2011