If only the graphics card is defective, then you should replace it.
If the defective graphics card is in a laptop/notebook, then you should replace the laptop/notebook.
For further assistance you would have to write which computer you own.
Well, you have to buy the graphics card separately. In my case, when the station is connected, it recognises several graphics cards (Intel, GTX960M, GTX 1080). But it should work. But overall, I would advise you to buy a new computer with all the components and assemble it.