In Malachi 3:10 God tells us that if we will bring ALL the tithes into the storehouse, so that there will be meat in HIS House, and prove Him, that He will OPEN the Windows of Heaven and pour us out a blessing that there will not be room enough to receive.
Could it be that He, God Himself, is interfering that until we learn the reality of tithing, and obey what He tells us to do, that the Windows are shut?
Pastor Darrell Huffman addresses this topic in this NEW four-CD series: "Opening The Windows of Heaven!" Learn from God's Word how you can receive all that God promises in His word! 
Titles in this series include:
Obeying God Doesn't Cost-It Pays
Bring Away The Hallowed Things
Are You Praying In Front Of Closed Windows
Giving And Confession