How do I find a video card for my computer?

It should be simple enough. I need a replacement for the one I have: 512mb nvidia geforce 95gs. But if I run a search online...I can't find it. I have a HP Pavilion Slimline s3700z desktop computer. I went to HP and the website says I should get a new fan...but doesn't tell me where to get one (I can't find just a fan on their site). I see other similar video cards...but how do I know which one to get for my computer? Is there a website that shows all possible cards for my computer?|||The only thing you really need to know is what type of slot you have for the card to go in. You didn't say which fan you needed to replace, but you can buy replacement fans online!