Aww, I hate when that happens!
I try not to force it, unless it's for a collaboration and I'm letting someone down by not getting my part done. If it's just one of my own stories, I let it go for awhile and do whatever I feel like doing. I try to read a lot, especially in genres that are similar to the story, in hopes of being inspired. Sometimes reading gives me the writing bug back. It doesn't have to be fanfic; usually it's published books that I'm reading.
Sometimes it helps to write something different. I always have a back-up story (or two... or five...), so I try that, or you could always try a challenge or some other one-shot. That doesn't always work for me, though; sometimes I'm just not in the mood, period.
Definitely reread what you have of your story so far, if you haven't already. If I've gone a long time without updating, I do that to refresh my memory and get back into the mindset of the story, and it usually helps.
I hope you're not gonna let freaking NKOTB kill your BSB love! Then they'd be doubly evil! That's even more reason to ignore all the NKOTBSB stuff and immerse yourself in fanfic, in a realm where NKOTBSB doesn't exist LOL.