I had been doing anal play for nearly 12 years before I even got close to my pspot. I got a propper prostate massager in the last year and did some exploring, i could feel something was close but for the most part the best I got was an enhanced ejaculation and some fun bum time.
It wasn't until I got a much higher grade massager that I really found out what I was missing. Specifically it was the Loki that brought me to the edge (review: http://www.lovehoney.co.uk/product.cfm?p=34253&reviewid=131747#customer_reviews )
That was the first time I had an anal orgasm and I think it had to do with a few factors. First of all I had an idea of what I was looking for, a little bit of experience goes a long way so don't give up hope. Secondly the size, shape, and power of the massager was just the right combination for me.
My best advice is to keep trying and maybe explore with different toys. Get youself excited and concentrate on the anal area. Hope this helps