pay close attention to the battery contacts, had cases where because of dirt of corrosion on either the battery or contact pins it can cause these symptoms. Try pushing the battery against the contacts to force a temporary good connection while prompting the console to boot and see if the symptoms change, then you’ll know if this is your issue 
I think I also had a case where it just didn’t like how the SD was connected and refused to boot (which doesn’t make a lot of sense) 
but cleaning it with contact cleaner resolved the issue