New phone - Only red/green light. No boot.

[Sloth]

If the battery is fully drained U-Boot might fail to boot any installed operating system on the eMMC and microSD card due to a bug.
If that's the case please start your phone in Maskrom mode and let it charge in that for a few hours. To do that:

• Remove any microSD card from the phone
  
• Hold the "RE" button underneath the back cover of your Explorer Edition (or shorting the bypass contact points on the Developer Edition)
  
• Connect the phone to an USB port of a computer, while still holding the button
  
• Check if the phone in Maskrom mode appears in the output of the Linux command lsusb on the computer (if the device disappears again please use a different cable)
  
• Let the phone charge for multiple hours
  

Note: If that didn't work, try to remove the battery and the USB cable and hold the power button for a few seconds and then insert the battery again, before retrying the procedure.

From the PPP Wiki. Hopefully that helps, I found just using a 5V 3A charger and waiting a bit also did it for me.