How to diagnose boot process of water damaged MacBook?

I acquired cheaply unibody macbook a1278 with water damage. I took it apart and cleaned it out with the alcohol. There are no visible damages or signs of the spill anymore.

The laptop doesn't really turn on. Whet I connect AC adapter, magsafe light comes up; it also charges the battery. However, when I try to turn the laptop on, the fan comes up, but there are no other signs of life. It's same on battery and on power adapter (with battery out); also I don't have a hard drive inside.

I tried connecting external monitor, keyboard and mouse (mouse's light come up briefly, then turns off right away), with same result (gets power - fan is on, but no chime/display/anything else). Same happens when I take out RAM. I also tried resetting SMC and PRAM, without any success. Disconnecting/reconnecting LVDS cable didn't change anything.

I guess that no start-up chime means that it does not finish POST. Are there any other things to check before I just decide to sell it as-is? I had some hope, because processor seems to be working (gets warm) and the fan indicates that the logic board turns on (to some extent), but since there are no other signs of life, I'm not sure where to go from here. Any help would be appreciated, thanks in advance!