It's an unfortunate situation you're in if you have such a small budget. Look, you can go and buy a graphics card and it may work. All people here are saying that with such a poor quality power supply like you have, and that's the fault of the manufacturer not you, they misled you totally with their 400w claim, is that this cannot be guaranteed to work or work in the long term should you install a higher powered card. Only 264 of those claimed watts can be used for the graphics card. So with that in mind and the fact that we don't advise people to disappoint them, we advise them with their budget and best interests in mind, nobody here can really tell you that what you want to do will 100% work.
Were you to be able to up your...