Unable to ajust brightness on IMAC G5

I have an Imac G5 that I am unable to adjust brightness on.  I have gone into system and than display and have adjusted the brightness but as soon as I let go it reverts back.  There is also a transparent icon on the screen that appears to be for brightness that when I adjust the bar at the bottom turns green.  This transparent icon has been there since yesterday and I am not sure how to get  rid of it.   Just to give you a heads up, the user spilled water on the keyboard yesterday and the keyboard was unusable.  It has since dried and is working again.  I do not have a spare keyboard to replace it.
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You may want to disassemble the keyboard and get rid of any residual moisture.I assume the problem is very much to do with the spill since it worked before.
There are some pretty small crevices in keyboard and residual water is a definite possibility.
Modern keyboards aren't just a bunch of switches either as people commonly think.
There are IC chips in there.,

To disassemble is probably best..
If you're not carefull you may discover the 100 and something keys is a lot of keys.

Next is to put it someplace very very warm with a fan blowing on the keys to evaporate the residual water out.

An extreme method is to disconnect the keyboard and flood/flush it with isopropyl alcohol (rubbing alcohol).
The alcohol captures the water and evaporates quickly taking the water with it.
The military uses this for electronics (even directlt on circuit boards) that have gotten drenched (even with seawater) and I can tell you first hand it works. (I once brought a CPU and monitor that had been dropped in a pond back to life with this though much disassembly was required to get to everything.)

After flooding it, and slushing it a little to get into the crevices, pour out all the excess you can get out, then set the keyboard on edge in the warmest VENTILLATED place you can find and ideally place a fan so it's blowing on the keys.
~ Leave it a day or more to dry. (Because of the crevices.) No a hair dryer won't do it for a keyboard.

Standard 70% isopropyl will work but 90-91% is much better (less water so it captures more) and it isn't too hard to find at drug stores.

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