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Remove all power sources and battery from the back of the laptop .
If the liquid is from the bad end of the spectrum, and will leave residues from (for example) milk and sugar, wipe the laptop down with a damp lint-free cloth.
When you have done as much as you can, leave the laptop propped up somewhere warm to dry for at least a day, and preferably for two days. Don't use a hair dryer, which will blow hot dust into a sticky environment.
When you are sure the laptop is absolutely dry, you can replace the battery and see if it starts. If it boots the operating system, does everything else work? If the keyboard doesn't work, try plugging in a USB keyboard: most computer shops and many supermarkets sell keyboards at very low prices. This may allow you to retrieve any data that hasn't been backed up.