find me the exact computer you have and give me the link, Give me a price range you are willing to spend and i'll find you one.

HMV wrote I have a dell optilex not sure what one I'm not really good with PCs so that's why I'm asking here does anyone know what graphics card will fit and work with my pc? +rep

We need to know you exact computer and price to find you a GPU.

Doubt you'll be able to add any GPU. It's a pre-built. Dell used to use BTX form factor, which is basically an upside down and back to front version of ATX. This means upgrades were a huge pain in the ass. If this is what you have, it's best to build a new PC. You'll most likely need a new case regardless and unless you have already upgraded the PSU, that'll also need an upgrade. Download Specyy and post a screenshot of your specs. We also need to know your case and PSU, make and model. After this, we need a budget and currency to find you a GPU.