My iPhone 4 won't turn on

My iPhone 4 won't turn on, or charge, when I plug it into iTunes it's not recognised. I've had it from new, and it's only a year old!

I've always taken good care of it, always had a case, screen protectors, no scratches at all.

I had about 90% battery, put it into my pocket and when I took it out it wouldn't respond! Won't turn on, won't charge, I've tried plugging it into the mains, and both of my laptops, still nothing.

Please help!