Step 23: Power
Plug your battery in and place it in the battery holder.
If all went well, it should now be turned on and making noise.
If it not turned on, try pulling the power switch. That should help.
If it's not working. Try a new battery.
If it is still not working, try to debug as best you can.
You did heed warning to the bold and italicized note on step 5 which said to make sure everything was working before moving forwards, right?