The EXACT same thing happened to me. Please help!
My phone is not rooted and it updated to JB while I was still in the store. I am hoping to at least recover my photos/videos. I had no music or apps on my card. I have very few apps installed from the Play store. I had not yet connected the phone to my computer since I had had it less than 10 days (purchased Dec 15th failed on the 23rd).
I'm just not sure if I should try to use the warranty to get a new phone.