What's in the pot is dead. IMO, the best would be to take off whatever is still alive. Get rid of all dead stuff. It needs to be planted in good, free draining mix - one that doesn't contain too much peat. Peat stays too wet for too long (or if left to totally dry up, becomes as hard as a brick).

This plant should root easily; get all the green pieces, stick them into better mix and they should root.

Whenever you water, all excess should be dumped out of the saucer after about 1/2 hour. If left sitting there, it will just keep the soil at bottom of the pot constantly wet and that is not good for roots.

Do what rina said, it is your only hope at this point. A good soil mix to try would be 60% perlite, and 40% cactus and succulent mix. Try that. It will work, but you will still need to be careful about watering.