What can people do when government is corrupt?

As john Locke said, you enter into a social contract with your government. Once that contract is broken, it is your DUTY to revolt and cause a revolution. This might not necessarily be a violent one, but it is your civic duty to protest against an injust government, like Egypt is doing right now. In face of a tyranous government you must challenge the authority and do what you can do remove the corrupt from power (ideally through legal ways). Civil unrest frightens governments no matter how strong they are. The governments serve their people and it is your responsability to remind them of that.