computer gaming build

Hey y'all! I got this desktop for 20 bucks want to upgrade it for gaming I'm on unfamiliar on how and what's compatible I'm willing to learn and buy the parts just need to be pointed in the right direction. It's a Lenovo 510a-15Icb desktop with Intel core i3 processor with 8GB ram. I usually...

My System is Following 1. CPU - i7 4790K 2. Mobo - ASUS Z97 PRO 3. GPU - AMD R7 260X Sapphire 4. PSU - Cooler Master G550M My PC stopped suddenly, i tried the reset button several time but it did not work. So i opened it and tried the paper clip method of the PSU. The Fan Runs. So i thought...