Okay, so you had to pull the motherboard to get to the left speaker, which means you had to unplug the keyboard.
Now I'm not an expert on the MacBook Pro models, but on the regular MacBooks, the power button is basically just another keyboard button that gets a little special treatment for power on and off. So if the keyboard isn't plugged in, the power button won't work either.
It rather sounds to me as though the keyboard connector may not be seated correctly; with those wide thin flex cables it's easy to get them off by just a hair and they don't work. So first thing to do is open it back up and carefully check the keyboard ribbon cable. Pull it out and clean it with some isopropyl alcohol, verify there's no damage to the cable or the connector. Carefully reseat it in the connector, making sure it's inserted fully into the socket before you flip the latch.
With any luck that's all it is and you'll be back up and running in no time!