Providing these water quality things are fine there is the chance that the cord running to the disposal has developed a short or a wire has become disconnected. You will need to disassemble the unit to verify all wires remain securely fastened. The last conclusion is that the motor has burned out, in which case you will need to replace the disposal unit.
Use the sandpaper to remove any loose particles from the hole. It is important for the surface to be properly prepared for these types of gutter water line repair.
One other common design that is considered "washerless" was made famous by Delta and copied by several other makers. It uses little "cup" seals that fit over springs recessed in the back of the valve body. The springs press these "seals" against the cartridge and regulate the flow through little tapered openings in the cartridge. If you have one of these and it's dripping, changing these springs and seals will usually correct it. Here's a tip. Once you have the cartridge out of the way, insert a phillips screwdriver into the seal and pop both the seal and spring out. Stick the new ones on the end of the screwdriver to help guide them into place. This is especially helpful if you don't have long slender fingers.
Working on the gas lines is also a complex job that only a licensed plumber can handle because it is very dangerous. Small leaks can't always be detected by odor alone, but a licensed professional has the proper equipment that's needed to ensure that you don't have any leaks in the line.
Remove the cap of the faucet using slip-joint pliers. Tape the teeth of the pliers to prevent damage of the surface. Remove the faucet cam washer and water line repair the rotating ball.
If you plan to replace fixtures, you may be able to do this on your own. Buy the same style or functional fit and then turn off the water to make the switch. Follow the directions provided by the manufacturer to get the job done.
Water leak detectors can keep your home safe. They can give you the peace of mind knowing that you won't come home to a house full of water. It is a lot less expensive to buy a water detector than it is to pay thousands of dollars in home repair costs.