I dont think there is any such thing as a good gaming rig that can run those games under $400. If you manage it you will be buying components that are cheaply made or have a high failure rate. You need a bigger budget if you want to run Cryisis. If you want to play Crysis on 55 FPS your video card will cost you nearly $400. Cross-firing shitty graphics cards is worse than buying a more powerful one. 4 gigs of ram......most laptops crush that. Your power supply has terrible ratings and is to low powered to run the system you already have set up. You need to rethink this PC from the ground up. I also don't see and graphics cards on this list specified for your acclaimed $400.
If you need help let me know man. Im glad you came to the forums before getting this stuff.
you will definitely need to improve your budget if you want to be able to play modern games at a bareable fps with decent graphics. You could make a decent AMD system for about $800 that would be acceptable.
One way you can get a decent system for cheep is to reuse the bulk of parts from an older one.
The main parts that get replaced are motherboard, CPU, RAM, and video card. If you have a copy of Win7 you already bought for a "whitebox" system then you can just use that.
If you want to upgrade on the cheep here is what I found on Newegg:
Motherboard: ASRock Pro4 Socket FM2 - $87
CPU: AMD A10 5800k - $130
RAM: G.SKILL Ripjaws X Series 16GB (2 x 8GB) 240-Pin DDR3 SDRAM DDR3 2133 (PC3 17000) (Item #N82E16820231571) I know 2133 might seam like over kill but the video card upgrade will come later so you need faster system RAM and it's not that much more.
Cooler: SILVERSTONE Heligon HE01 - $65 after $10 rebate or $60 for open box
Later on down the road you could add an AMD/ATI video card and crossfire the APU one with the added one. The main reason for the faster system RAM is that it doubles as video RAM. Might seam like the same as regular integrated but unlike integrated it has it's own cores on the CPU die and it's own memory lanes instead of using the main system memory lanes like on normal integrated.
Update: I just checked the hierarchy chart here on Tom's Hardware for this month and the "hybird" video of the A10 5800k APU is the same as a GeForce GT 440 or Radeon HD 4650 discrete video card.