Ran into a problem with my Lenovo T400. The laptop would not power on. No lights of any kind. Tried with and without the battery and/or AC adapter. Found these instructions while searching around for a solution:

  • Ensure nothing is plugged into the computer
    • Remove the battery
    • Press power button 10 times
    • Press power button down for 30 seconds
    • Press power button twice
    • Attach ac adapter
    • Press power button once. PC should come up. Perform normal start up. Everything should be fine.
  • Shut down and reinstall the battery

Worked like a charm.