New Screen but the screen won't illuminate.

Hi,

I recently replaced my own personal phones screen after it was cracked. I have replaced phone screens in the past so I knew that the iPhone 6 screen replacement is a breeze and I am familiar with common issues relating to that repair. I, however, went to turn the phone on after it was repaired but the screen didn't light up. Consequently, I opened the device again, double checked that after thing was properly connected (which it was), closed the phone back up and tried to start it again but it didn't work. I plugged the phone into my computer and it still didn't light up or vibrate but my computer recognized it with no problems. I held down the home and power button to force restart it, replaced the battery and tried a variety of other techniuques to force it on but the screen stayed black. Any advice?

Extra info: All parts were ordered from the iFixit website store.