Have you tried remotely testing it? As in using a different power source? Just seems like a hiccup if you're not getting any power. Maybe even a sensitive amp. I know my kenwood deck would give me errors all the time when I tried to install it. Wether I'm wrong or right about how I fixed it, I THINK there wasn't enough continuity within the speaker wire. I cut the the wires shorter and had less wire available, worked after that. I use to hook up amps and subs for testing with various speakers and such. I say start with the power source though.
have you tried taking it to him first and asking him to check out the repair? if he's not going to, follow the guides for a full tear down and try it yourself. Maybe some things are loose as in the connectors and battery. If he missed some screwed or didn't make sure things are secure, you'll have those issues.
Sorry if this post came up more than once, my internet kicks out every time i submit. If the phone vibrates, its got power. Its 1 of 3 things. 1. The LCD you bought was shipped broken, the testers are cheap. Wouldn't be bad if it saves you $40/$50. Please don't buy cheap screens. You'll notice the difference in the display. 2. The flex cable is loose. Take it apart, disconnect and reconnect the cables and make sure they're snapped down. They should snap, sometimes there's a little yellow tape on the LCD that gets moved from holding down another component. Make sure the motherboard and the cable itself has nothing in or around it. 3. You probably ruined the LCD flex while installing the glass. Those cables are thin, and can easily be ruined. Hopefully its not the case. I've been repairing phones for years, i've accidentally ruined a few while rushing.
have you tried 1. toggle the vibrate switch. Does it vibrate when you press down? lift it up and down on a series of times to see what happend 2. plug it up to a charger. sometimes the sleep button or a home button doesn't work. Troubleshooting will start with there. If your volume switch is up, you'll hear it make the "charging sound" 3. Take it to an apple store, if it hasn't been taken apart or opened 4. If you've dropped it, you might of cracked the LCD and not the glass. Try the beginning steps first. Front glasses are between $30 and $70 for high end ones that are colored. This is the last step
you can find the actual battery connectors for sale. Soldering them off/on is a different story. I'm techy, i forget the basics of soldering, i tried and failed. But for not backing up my iphone, and it not staying on, it was worth the $50 at my local shop. Sometimes we can't fix it all on our own