Ouch, a watered-damaged MacBook! Maybe someone spilled some water or other liquid onto the keyboard. This is bad! Immediate action is in order, with seconds to spare.
This is how I address a water-damaged device.
TIME IS OF THE ESSENCE!
- If it still works, turn it off immediately!
- Make sure it is unplugged. Don't plug it back in.
- Do NOT try to plug it in or turn it on again. Really.
- Open it up. This requires the appropriate precision screwdriver kit. Don't have one? Take it to a shop! Do NOT use the wrong tools.
- Disconnect the battery
- Mop up any water with paper towels.
- Is there water everywhere? Pull out the board and other components to do some further mopping up in the tight spaces.
- Put the parts, except the display and battery, in a slightly warm oven (maybe 90 °C, or 190 °F) for 4 hours to help encourage the drying of parts. Water can get under components, we want to encourage that water to evaporate.
- Let everything cool, reassemble, and test.