It may be, remember, that God has indeed answered but not in a way that is obvious to us.  And it is possible that nothing is amiss in our praying, but that we haven’t yet seen the answer only because God intends for us to persevere in praying about the matter awhile longer.  But we must also learn to examine our prayers.  Are we asking for things that are outside the will of God or would not glorify Him?  Are we praying with selfish motives?  Are we failing to deal with the kind of blatant sin that causes God to put all our prayers on hold?