Your switch is fine
The switch is fine -- it just needs to be wired correctly. Keep the neutrals nutted together, and pigtail the ground to the switch's ground terminal (I have no clue why a black wire got landed on a ground screw in the previous configuration, but it was clearly wrong). (You can strip your existing 12AWG white pigtail bare and reuse it for pigtailing the ground, BTW.) Then take the feed (3) and the bathroom (2) black (hot) wires and nut them together to your black pigtail, which lands on one switch hot screw. Finally, land the remaining black wire on the other hot screw.
I hate to put it this way, but you are in way over your skill level. I highly recommend getting a professional electrician to help at this point.
You connected the ground wire that to the switched hot. When you turned on the switch, you
shorted the circuit. That should have caused a fuse to blow or a breaker to trip. Based on "I tried doing the fuse box it didn't work.", you either have not found the correct fuse or breaker, or some part of the electrical wiring in the room (possibly at the switch, possibly at an outlet) burned up (literally) and broke the circuit.
Hopefully a fuse or breaker did trip - if not then the safety of your fuses/breakers is questionable. But even if you find the fuse (and replace it) or breaker (and reset it), there is definitely a possibility of damage due to arcing in any/all of the devices on that circuit (switch, receptacles, any wire junctions).
Now for the educational part: Most circuits have a hot wire, a neutral wire and a ground wire. Normally (there are exceptions in various situations), the hot wire is black or another color besides white, gray or green; the neutral wire is white or gray; and the ground wire is green or bare copper. There are a number of situations where the ground wire is not connected - particularly switches. In those situations, there still should not be any loose ground wires - they should be connected to each other, to metal boxes or capped - they should not be floating around loose as you found. Simply connecting wires "because it is there" doesn't usually end very well.
As for your specific original problem, my hunch is you have a fluorescent light that needs a new ballast and/or starter and/or bulb.
Best Answer
This is a serious electrical risk. You (and your kids) cannot afford NOT to have an electrician come and check out this dangerous situation. Attempting to bypass the problem without expert advice risks fire and electrocution.