Why is there a blinking question mark folder appears

Ummm, if the MacBook is acting up like this, then something definitely happened.

A blinking ? is a sign of NO BOOT DEVICE. That's no Hard Drive is available to boot from.

Sounds like that water did get in there and it got to the connector for the hard drive, which is very close to the trackpad underneath.

I would get that opened up and looked at. Leaving it for 4 days may have done it in, whereas if you had gotten in there and dried it out with a heat gun or hair dryer you may have been able to save it.

Good luck, this kind of sucks and I hope you get it running again.

Mike

You could try installing a new OS it might fixit but thats usually a sign of a Hard Drive Failure but because of the water damage a hard drive replacement still might not work I would sagest a water cleaning as soon as possible to prevent corrosion on other parts of the computer and it might even save your computer.