That PSU is plenty powerful enough. Have you made sure you've plugged everything in? Do all of the fans spin up (case fans, the CPU cooler's fan, GPU's fan, PSU's fan)? Did you attached the heatsink properly?
Really, that's about all we can do for you. That and point you to the standard troublehooting thread. The link's in my signature. That will cover nearly everything that can cause a build to not boot properly.