400$ budget pc suggestions?

Just make sure that whatever you buy, that everything is on the same level.
Remember your computer is only as fast as the slowest component, which usually is the hard drive (if it isn't a solid state). But on a 400$ budget I wouldn't be too worried about a Solid state drive, since you can always upgrade it later. Just make sure that you don't end up spending like 300$ on the CPU and graphics card, and then 50$ for your motherboard and RAM. Make sure you get a decent motherboard, since it is what links all the components together, you don't want it to slack. I'm not saying go look for the most expensive one, just try get one that is in the same class as the rest of the components. Also keep in mind that you can always buy more RAM later on, but to upgrade components like a gfx card you need to buy a whole new one, so 4GB of ram to start with should be more than enough. Also when buying a graphics card you need to understand that nVidia or ATI only manufactures the chip (The GPU [The processor]) and not the card as well, so what happens is other company buys the GPU from ATI or nVidia and puts it in their card. This results in that you have cards with the same model number, but different brands and prices, and the performance is also very different. So basically don't go looking for the cheapest brand, get yourself something decent like Gigabite or Asus, I'm not really that up-to-date with the different manufacturers and their performance, but just go on Google and make sure the brand you are buying is decent (remember if a card is a lot cheaper than another one and its the same model just different brands, the more expensive one will usually outperform the cheaper one by far).

Also don't trust the advice of a salesman at a PC shop, no offense but they are there to make a sale, not set you up with the best you can get, so they might sometime try get rid of old stock etc. Etc. So just be careful.