Brake Light!!!! Help!!!

Ok i was on my way to work today and all of a sudden the brake light comes on. I added new brake fluid like a week or so ago and now it seems to be leaking. I need new rotors i know that. I just wanna know why its doing this. Could it be something major, it never did it before.

Also....

I thought it was just the low brake fluid, but i went to wal-mart to buy some, and i pop the hood and unscrew the master cylinder cap, and the rubber was blown up lke a baloon. so i fixed the dents, and put the cap back on and turned the car on, and the light didnt come on. THen i let the car sit for few hours and go turn it on and the light is on again. please help.

I dont know if it matters i added DOT 3 fluid.

I also see that the driver side fron rim on the inside has fluid on it, and so does the inside of the tire..the tire looks like it has tire shine on it.. and the front driver side rotor is the one i really need also