Cant power Ramps 1.4 via PSU. D2 Diode installed

Hey everyone. I have a prusa i3 with Ramps 1.4 and cannot get it to power on without plugging the Arduino into a 5V USB power supply. I have both diodes (D1/D2) installed and I have a 12V 30A psu purchased from Amazon (http://www.amazon.com/Universal-Regulated-Switching-Computer-Project/dp/B00D7CWSCG/ref=sr_1_1?ie=UTF8&qid=1397876792&sr=8-1&keywords=12v+30a). I also have a reprapdiscount smart controller am able to print when not connected to my computer, but absolutely need to be connected to a 5V wall charger. I just replaced both diodes today and still having the same problem. Offline printing once worked but I feel like it may be that I added too many AUX electronics (auto level servo & LCD). Does anyone have any possible suggestions?
Thanks

Is the diode installed in the correct direction? Also possble the voltage regulator on the mega is blown. Did you check for voltage on both sides of the diode?

Also of note: There are a bunch of Mega clones out there that don't connect the pin RAMPS supplies voltage to the Arduino on to the actual input of the regulator on the Arduino Mega.