Only 1 way that's going to happen on $400 budget is very tight shopping on eBay. You can get a decent pc for $400, but when it comes to a decent gpu, its very easy to add a further $200 to that. Even brand new Walmart pc's or Sam's club, at the $400 price range usually do not include a dedicated gpu, relying on an APU, with its igpu or an i3 with hd4000, neither of which will be anything more than low-medium in 1080p.
My build from ebay:
MSI mpower z77 $50
I7 3770k $50
Nzxt Kraken x61 $40
Fractal design r5 window $30
Patriot 2x4Gb 1866MHz ram $20
That was the easy part. New gtx970 $300, new Evga G2 550w $80
$190 for the build, $380 for what I refuse to compromise on. Total = $570 for a pc that will destroy 1080p on ultra.
For medium-high settings, look for a r9 270/270x, gtx660, and a good 520-550w psu.
If you shop smart, it can be done, but it will take time, took me 4 months, but saved me @$800