The GPU sounds like it was damaged when your previous configuration was damaged. Based on what you have provided, I see no other option for you other than to replace the GPU.
To verify whether it is defective, try it in another system. Or, try another GPU in your current system.
In a system like yours, the on-board video adapter is automatically disabled in the BIOS when you install a stand-alone video card (like your 9500GT) . If your on-board video still works properly with the 9500GT installed, that is another indicator that the 9500GT is defective.