Liquid damage is why your laptop won't turn on. Just a little bit of water on the system board creates areas of corrosion that cause parts to fail. What you should do for a liquid spill is to disconnect the power adapter, remove the battery if possible and let it dry for at least 24 hours. If the computer is out of warranty (liquid spills tend not to be covered under warranty) and you are confident enough to remove the covers and use alcohol pads to clean up the spill. Alcohol will mix with the liquid and pull the moisture out as it dries.
The good news is that generally the hard drives will survive a liquid spill, although not always. You have a decent chance to recover your data.