Considering nothing burnt when you connected to the computer the first time, there are few things you can try.
Biggest problem I think is that even you think you have cleaned it out, it might be wet yet in some parts of the electronics. The easiest thing you can do is to let it dry for days.
You can try few things…
- Put it inside a container and dig it into rice. The rice will take the moisture from the interior.
- Put it inside a sealed bag with lots of silica bags. As the rice, the silica will take the moisture from the interior.
- Put it in a warm place so it reachs 30~40 ºC. For example you can put it in contact with direct sun light for some hours, let it warm a bit to later put it back in shade. Repeat this steps several times during several days. Be careful and don’t let it get too hot. Don’t even consider to put the keyboard in the oven or the microwave!!
Once you are completely sure the keyboard is dry, try to connect it again to the computer. If you are lucky and nothing is broken, it will be detected and working again.
If you are completely sure that the keyboard is clean and dry. Ideally you would like to clean it with IPA (Isopropyl alcohol) to clean the electronics from any rust, oxide or minerals that might be causing a short. Use a soft brush (a toothbrush is fine) and gently brush everything with the IPA. Let it dry well.
If still not working…well, there’s probably some burnt part. If that is case, the debugging work is more difficult as you will need to use an oscilloscope to check which part is not working as it should do.