is a power option set through the System BIOS and through the Control Panel applet. Try RE-SETTING the power options.

You mention "the day before I tried shutting it down and failed, I spilled a bit of water (less than half a cup) on my laptop while it was asleep" and that is most likely the actual fault and cause of your problem - even a single drop of water in the wrong spot is more than enough to cause problems ranging from glitches to actual arcing shorts.

I would suggest positioning the laptop so any moisture could drain from both top and bottom and set it in front of a fan blowing air from a floor heat vent for a couple of DAYS as it will take some time to dry areas that can't directly be reached.

As far as manually turning it on and forcing a manual shutdown by holding down the power button, that is how it was done before auto shutdown was available so the only damage you might see would be increased usage of the power button.