事故 is an accident and 事件 is a problem!xD

事故 refers to something that happens out of carelessness or by merely coincidence such as 交通事故（こうつうじこ=traffic accident） and 飛行機事故（ひこうきじこ=plane crash）. Whereas 事件 is something caused by people, mostly violent and harmful, such as 強盗事件（ごうとうじけん=robbery） and 殺人事件（=murder case）. I hope this helps.