My son knew that he wasn't suppose to bring drinks near my computer, and he didn't listen! Now he spilled water all over my gaming computer and it won't turn on.
Oh no!  That would've made me so mad.  I let my kids use my computer too but always say, no drinks by it and wash your hands.  Kids always seem to forget that. 
I'm not so sure if it's forgetting or just wanting to be contrary, honestly! Maybe I'm just being a little negative because of how mad I am. People do make mistakes, but that computer cost me and arm and leg to build!
It is a hard balance because they need to learn and it should make you mad, but people do make mistakes.  So hard to know how to act really but things are too expensive to not treat them well.  I hope you're able to find an easier way to fix it.