Just wanted to come here and comment as I had the same problem and fixed it. The battery report suggestion worked well! I have two internal batteries so I thought it couldn't be a battery issue - surely both batteries wouldn't fail simultaneously. Turns out it doesn't matter, the batteries must be wired in a sequence that if one fails it disrupts the power state of the system, preventing boot-up without first doing a power drain, despite the other battery functioning properly. Hope this helps somebody