Computer not starting up after installing new PSU

I decided a few weeks ago to upgrade my computer so that it may run a few games that I like on PC (Skyrim, civ v, many others). After installing both a new PSU (EVGA 600B) and graphics card (Sapphire Dual-X R9 280) to my HP Pavillion p6687c, it will not start at all.

Now just so you know, I am not too familiar with the structure of a computer. I followed the installation instructions and watched several tutorials on what plugs in where, all to end up with eagerly attempting to turn on my new and improved computer and failing. I plug it into the wall, flip the on power switch in the back which lights up a green light in the tower, and push the on/off button with no response, not even the fans start up. Did I fry the MOBO? Is it a faulty PSU? I'll test tomorrow to see if my old PSU works, hopefully someone could give me some advice other than that. I probably shouldn't have gotten into buying parts for my computer until I had a full understanding of how it all works... I just really wanted to game heh. If you need more information in order to help me let me know!

 

Hi and welcome to TSG.

First thing to do is, as you said, put the system back to its original specs (old PSU back in and new GPU out) and see if it runs. Damage is a possibility and a fault PSU is a possibility.