iMac 21.5" - New Power Supply, powered up once then nothing

My mid-2014 iMac was having intermittent power issues (would only turn on sometimes and then would randomly power off) until one day it was unresponsive completely. I replaced the power supply and when I did a test start with the screen plugged in (before adhesive) it powered up fine. Once I put the adhesive on, the iMac will no longer power up at all. Diagnostic LED #1 is lit up with power plugged in.