After replacing back case my phone doesnt fully power on

So i replaced the back casing on my phone following the tutorial from this site, as well as an identical video tutorial on youtube. I got everything to fit nicely and got it all closed up, but now when i try to power it on the backlight turns on for about 5 seconds then turns off. I dont believe the phone is powering on at all, and when i plugged it in the screen lit up yellow. from these signs could someone maybe tell me what i might have messed up when reassembling my iphone/what these signs usually mean.