Chosen Solution
MacBook Air 2013, would not start, took it apart, dried out water and cleaned solder points with isopropyl alcohol 99%U.S.P., tried restarting it and it started once, but computer screen wasn’t working, worked with a monitor connected, shut it down, charged it overnight, it won’t start now. Any ideas?
Check you just haven’t blown the backlight. Shine a torch on the screen and see if you have an image. I have found if you remove the SSD and shine a torch at the back through the apple logo is best as this is where the flashing folder will appear. If you can see an image this would mean a component on the backlight circuit has become faulty. Depending on your skills and equipment and what component has become damaged will determine if you need to send it to a repair shop.
It sounds like the main logic board may have damaged sensors or shorts due to corrosion from liquid damage. Liquid damage repairs can be complicated and there is too little information here to offer a good fix. Your best would be to take this machine to a repair shop that specializes in logic board repairs.
