Re: New 15i won't fire
I have no doubt PSE will easily replace the entire trigger mechanism. They are very good about replacing faulty parts on these crossbows.
The thing i wanted to suggest to you is you may want to consider replacing the factory trigger with a Timney AR15 competitive trigger. Len and Andy are distributors for Timney and sell them in their shop. There price is the same as you'd pay if you ordered from Timney themselves.
The Timney Triggers are are much lighter in pull weight than the factory triggers and they have no creep, so they are a real pleasure to shoot compared to the factory trigger system.
If the price is an issue most people would tell you to save up your money and make the change when you have it because it's one of the most important modifications most shooters perform to their TAC15 / 15i's.