MacBook kernel panic error screen on boot
You should take the computer in to your local Apple Store or Apple Authorized reseller. It may be that the milk (or milk residues) finally dripped down enough to short out parts of the motherboard.

Don't try lying to them; fess up to the milk spill and maybe you'll get lucky. In any case, you're looking at what is likely to be an expensive repair (involving the motherboard, keyboard, and anything in between).