It's hard, and it's frustrating year after year to know that Purim has lots of spiritual potential and koach hatefilla, to daven a lot, and not see fruits of your labor.
First of all, Adar is actually an awesome time to tap into these feelings, because that's really what the whole Purim story is about. The question is what is this simcha that we're supposed to be feeling during Adar? To quote a summary of a shuir by Rabbi Wallerstein, "It's the happiness that comes from the realization that what looks dark and dreary, is really light - and something positive will come out of it. It is not natural happiness; it is supernatural happiness. It is the pain and struggle that we go through that gives us the ability to grow and achieve. Esther’s struggle, as hard as it was for her, was what saved Klal Yisroel in the end."
Also, I heard a true story about a girl who was in shidduchim who heard that it was a segula to say the whole sefer tehillim on Purim. She stayed up really late Purim night saying tehillim, and nothing. She waited the whole year certain she was going to get engaged and she didn't. The next year, on taanis esther her uncle called her and said, "You know, it's a segula for a yeshua to say the whole sefer tehillim on Purim..." She just wanted to hang up on him and go to sleep early instead of staying up saying tehillim, because it hadn't worked for her last year. But, she decided to try again. She said the whole tehillim Purim night, and she didn't get engaged that year. A year later, it's Purim and she's not really in the mood to say the whole tehillim, let alone daven at all, because it hadn't really gotten her far. Against this judgement though, she pushed herself and said the whole sefer tehillim. That year she met her chosson. And so, the next Purim, she was happily married, and her husband said to her, "You know, Purim holds a special significance for us." She was a little confused because she didn't think he knew about the 3 consecutive Purims that she had stayed up really late saying the entire sefer tehillim. When she asked him what he meant he said, "Well, three years ago I was kind of goofing around, wasting time, not really doing what I should be. On Purim though, I had this inexplicable strength to buckle down and really learn. It lasted me until Shavuos, but after that I kind of just lost it. But the next Purim, again I felt this added strength and I was able to really focus on my learning. This time it lasted me all the way until Sukkos. Last Purim, I again was able to pick up this strength and learn like I really wanted to, and I'm learning like that until now. It's Purim that brought us together. If it weren't for the realizations that I had and strength I was able to tap into on Purim, I wouldn't be who I am today and we wouldn't be married."
Moral of the story, you never know what your tefillos are doing. It may look like they're "not working," but we can't see everything. Maybe it's just one more tefilla that needs to be said in order to bring your yeshua!