Some ac adapters will go into protect mode and stop providing power. Try unplugging the power adapter from the wall for a few minutes, then plug it back in and try to power the computer on the ac adapter alone.
If it still does not work, use a multi-meter to test the output of the power adapter to make sure it is providing power. If the adapter is outputing power correctly and the computer still does not work on the power adapter:
ElfBane is correct, if the computer has completely dried out and still does not function correctly the motherboard may need to be cleaned, this requires a full tear down. I recommend using isopropyl alcohol at 90% if you can find it instead of distilled water. Alcohol dries much faster than water, 90% dries faster than 75% and it also seems to clean better than water.
Also if the liquid was spilled when the computer was on or if the computer was powered on while the liquid was not dry, it may have caused permanent damage to the motherboard. From the sound of it the charging circuit may have been damaged. If this is the case replacing the motherboard would be the only option to continue using the computer with the power adapter.