$400 PC Build?

[MUSE_iC]

So im wondering if I could possibly build a gaming PC that can play games on High (like Dark Souls) for a budget of $400.

What I already have:

Monitor
Mouse and Keyboard
HDD
PSU
DVD Drive

Im not sure if the PSU I have would need to be replaced to suit the needs
So here is some info.
+12V1@18A, +12V2@18A, +12V3@15A
All at 450W
The brand is Coolmax.

What I need:

CPU:
GPU:
RAM:
CASE:
MOBO:
PSU (if mine isnt good enough).

$400 would be my spending limit for the missing components. I could go up to maybe $415.

 

[MUSE_iC]

I just took a look over on PCPartpicker and they coincidentally built a budget PC for a Reddit user.

http://pcpartpicker.com/blog/budget-gaming-build-core-i3-2120-radeon-hd-7750

If I take out the items that I already have it comes outs to $375.27.
The left over funds could be used for improvements in another area like graphics card or processor.
It also comes out to $335 giving me a bit more to spend if my PSU can do the job.