You can replace the circuit breaker. The main breakers are very hard to push and you apparently have an old one and the plastic was brittle. You need to know what kind of breaker box it is and take it with you and if it isn't too old the hardware co may have one or an electrician can tell you where to go. He just might help you because the job is really minor. The major problem is the short in the broken breaker.
Only one suggestion-call in a licensed, certified, insured professional, and do it as soon as you possibly can! You have an overload somewhere and by forcing that circuit breaker over you have worsened the situation. This is a fire waiting to happen, no kidding, this is VERY serious.
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