Liquid damage, not booting up

I spilled very little tea (without sugar) near the power button. I immediately powered down the computer. It worked perfectly during this 5-10 second process.

I then put the Mac facedown, opened it, disconnected the battery (and the little thin and long ribbon cable over it, which I'd like to know what is for). I noticed that the logic board was not affected by the liquid (both face up or face down). No sign of liquid corrosion even one week later. There was some tea on the fan and underneath it, which I dried asap.

I waited three days before trying to see if the Mac was working again.

It doesn't start up. When I connect the power, with both the battery and the ribbon cable over it connected, the fan remains still. When I disconnect the battery and the ribbon cable, the fan starts moving and the logic board gets hot, but the screen remains black.

I thought that the keyboard was the only damaged part, but if it were so, booting should be possible by connecting it to outside power, right?