Well theres a couple reasons why it might not be working.
One of them is a broken circle, sometimes when you break a circle (stepping out of it, not casting it right, bringing negative thoughts within the circle). So make sure you're casting it well.
Also, you may need to do meditation before your spells to clear your mind. You can take as long as you like but it shouldn't be less than five or ten minutes.
Or the spells just may not work. Sometimes that happens, usually with spells that are more 'fantasy'-like.
The spell just might not be good for this time and the Gods and Goddesses don't feel as though they should send it through.
If a spell doesn't work its okay. You can always find another one. Just try to cast spells when you're in a good mental state. being depressed or angry will affect your magic.
So take it one spell at a time.