My current build is this And i am able to play games at High Heading into some ultra settings
AMD Athlon(tm) II X4 630 Processor @3.3ghz Stock (2.8ghz)
4GB DDR2 Ram @800mhz
SSD = Samsung 840 PRO 128GB
HDD - Don't know the mode but it's 7200RPM 1TB
GPU MSI Radeon R9 270 2GB
You should get an Intel processor i5 or better, they perform better, and upgrade to 8GB of ram, this should be plenty for gaming. Also, dont forget to get a good quality PSU, like Antec, Corsair, Coolermaster, etc, that are 80 plus certified.
The Corsair CX units are crap, they use capacitors that tend to fail under load.
Your current PSU should be able to handle this upgrade since the new CPU uses less power than the old one. Get a better GPU and PSU when you can afford it: PCPartPicker part list / Price breakdown by merchant