Alright. If you're either willing to use Windows 10, or have another way of acquiring an OS. AND you live within range of a micro center. You can pull off a better PC for $400 that may chug along for 4 years at medium settings.
PCPartPicker part list:
http://pcpartpicker.com/p/y2PQNG
Price breakdown by merchant: http://pcpartpicker.com/p/y2PQNG/by_merchant/
CPU: AMD FX-6300 3.5GHz 6-Core Processor ($89.99)
Motherboard: Gigabyte GA-78LMT-USB3 Micro ATX AM3+ Motherboard ($0.00)
Memory: PNY XLR8 8GB (1 x 8GB) DDR3-1600 Memory ($53.98 @ Newegg)
Storage: Western Digital RE3 500GB 3.5" 7200RPM Internal Hard Drive ($36.00 @ Amazon)
Video Card: EVGA GeForce GTX 750 Ti 2GB Superclocked Video Card ($124.99 @ NCIX US)
Case: Diablotek DIAMOND ATX Mid Tower Case w/400W Power Supply ($29.99 @ Micro Center)
Total: $334.95
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2015-03-03 15:55 EST-0500
This is stretching your budget as much as possible by getting a free Mobo with purchase of CPU at microcenter. You will need to provide your own peripherals. You might be able to save a bit by getting open box/refurbished parts.
At $400 you will not get a high end PC no matter how hard you try, but here's the best I could put together.
It's not bad actually. Other than the lack of extras, and a questionable PSU bundled with the case. But it will not be a powerhouse that will crank the graphics up.
Spend the last 70$ either upgrading the case/PSU, or on an SSD or something else.