Was is because of the Great depression that left so many people unemployed, and Hitler promised to solve their problems?

In short. Yes. In this, he was aided by the current Chancellor himself (unwittingly). Chancellor Heinrich Brüning wanted to lift Germany out of the Great Depression and establish a stable parliamentary government but could not get the majority vote in the Reichstag for many of his measures included in his financial program. So, he went to the President, Von Hindenburg and asked him to invoke Article 48 (giving the President emergency powers) and approve of Bruenings financial bill. The Reichstag fired back with a simple majority vote, nullifying the President's emergency decree. Thus, with only one option left, the President (with the urging of Bruening) dissolved the entire Reichstag and called for a new vote for September 14.

Now we come to Hitler. Also note that by 1930, some 4 million youths had come of age who now had the right to vote.

"To all the millions of discontented Hitler, in a whirlwind campaign offered what seemed to them, in their misery, some measure of hope. He would make Germany strong again, refuse to pay reparations, repudiate the Versailles Treaty, stamp out corruption, bring the money barons to heel and see to it that every German had a job and bread."

And so, when in 1928 had polled 810,000 votes and gained 12 seats - in 1930 he gained 6,409,600 votes and gained 107 seats.

With that, Hitler also gained the attention of the Army and the industrialists, who would later on be a huge help in Hitler coming to absolute power.