You have to ask with the right motives and it has to be within God's will.

(James 4:1-3 NIV) What causes fights and quarrels among you? Don't they come from your desires that battle within you? {2} You want something but don't get it. You kill and covet, but you cannot have what you want. You quarrel and fight. You do not have, because you do not ask God. {3} When you ask, you do not receive, because you ask with wrong motives, that you may spend what you get on your pleasures.