Chosen Solution
I replaced the battery in my computer. I charged it until the orange light went off. I then unplugged the power adaptor and tried to power on the computer pressing the power on key. Nothing happened. I plugged the power adaptor back in and pressed the power on key. It came on with no problem. Why does the power on key not work with a fully charged battery but work OK with the power adaptor connected? Could a wire have become detached on the motherboard when I removed the back to replace the battery?
Solved my problem. It was an error on my part. When I re-attached the keyboard ribbon, I inadvertantly had the slide lock on top of the cable instead of under the cable. Discovered this when the computer wouldn’t turn on at all - battery or power adaptor. Took it back apart and saw the problem. Battery now powers on the computer just fine. Lesson - pay better attention when disassembling the computer - take a photo.
