Economic - During World War 1, the German economy was completely decimated. Massive hyperinflation there is so terrible that when employees receive three daily paychecks, their spouses merely spend the money on everything they can since prices are so high. And although its economy was in ruin, Germany had to provide reparations to the people it was fighting. And to top it all off, there is the great depression.
Political - Although it is far from the truth, the Treaty of Versailles forced Germany to take full responsibility for the war. The pact also required Germany to lose a sizable portion of its territory to neighboring nations including Poland, France, Belgium, and a few others. German speakers and people of German descent populated several of these countries. It becomes worse since one of Woodrow Wilson's 14 principles called for self-determination for all nations save Germany, including Austro-Hungary, a German ally.
Social - The aforementioned political motives caused many Germans to feel exploited for other people's political objectives. So it should come as no surprise that they chose a radical candidate when you repress a people like that.