Hi Christian, I'd definitely check the I/O board first. It looks like the power from the charger isn't reaching the MacBook. Check the I/O board cable. If that doesn't help, I'd also check the battery. It's pretty unlikely though, because the MacBook should run off external power if a charger is connected, no matter if a battery is available or not. But you never know.
I'd recommend to use packaging tape to attach the upper edge of the display to the back of the phone so you won't rip off the ribbon cables if the display suddenly comes loose.
Doesn't the ATV control the TV via HDMI? I don't think Apple uses infrared, so you shouldn't need to be in the line of sight as mentioned in the article.
