Hi there. If you think you have an electrical issue make sure you take all precautions you can, including don't touch anything wet!
I couldn't imagine an on/off switch on an airstone. I guess you're talking about the pump there, which I have also never seen an on/off switch for, but I think you mean you turned your air pump off? And water backed up into the pump? Then did you turn the pump back on while it had water in it and it smelled funny?
I'm going on the assumption that that is what happened. It would make sense. It would indicate that your pump isn't strong enough for what you're using it for, if it can't push the air through the stone. It could be that the diaphragm in your pump has broken completely. It can happen, and when it does, it doesn't pack much of a punch (or any, really). They can also weaken without completely breaking.
I don't know if I'm too late for you here or not, but I would recommend as a course of action to grasp the cord in a dry place and unplug your pump. If things are too bad turn the breaker off first. I don't know where you live but here it is the middle of the night (eastern US) so you won't be able to go out and buy a new pump or replacement parts. Hopefully you don't have fish with high oxygen requirements and they'll be OK until morning. If they seem to be having trouble from lack of oxygen the only tip I can give you is that cooler water carries more oxygen, so unless you're already at the bottom of their temp. requirements turn your heater down. For instance if it is a typical tropical community and you keep it at 79F, go ahead and turn it down to 75 or 76F. Just don't go too cold or you'll stress them out more.
I hope I hear in the morning that everything worked out fine.
And welcome to the forum.
I hope you stick around.
EDIT: I just reread your post and noticed that it didn't get into the pump. If that is the case I have no idea what the smell could be from, but the broken diaphragm could still be the issue preventing it from pushing air through the stones. If water is only in the plastic tubing and dripping on the floor I can't see a reason for a funny smell.
However, if your pump is dry you can still try to use it. See if it works without airstones. It might still put some bubbles out, enough to agitate the surface a little bit and help with oxygen exchange.
And I maybe should add that seldom do fish depend on an airstone for their very lives. If they seem to be doing poorly it could be for some other reason, such as water quality. Do you know if your tank has cycled?
