I struggled with a similar issue for years! I had lots of story ideas, but every time I sat down to write I would get all over-critical, frustrated with not getting it perfect on the first draft, etc. Had hundreds of pages of plot synopsis and character sketches, but no actual books to show for it.
Then I discovered NanoWrimo. I read the book, No Plot, No Problem by Drew Curtis and visited the website,
www.nanowrimo.org. Basically, it's a crazy event where you write a 50,000 word novel in just 30 days.
Within 3 months of reading his book I had written 2 novels and I wrote another one last year. I'm currently working on re-writing so that I can shop for an agent.
The magic of giving myself a crazy deadline freed me from worrying about getting it 'perfect' (even an experienced novelist will tell you that's impossible) and let me just get it done. After the 30 days I had an honest-to-goodness complete first draft of an entire novel which I could then go back and work on. Much better than just having an idea for a book!
If you are interested in writing at all, I highly recommend trying this event. It's a lot of fun and it's one heck of a productive writing month...plus you get to meet lots of other writers!