iPhone 4 won´t turn on, apple logo blinks

When I woke up this morning, my iPhone 4 said that I had to activate it by connecting it to iTunes. I had no computer nearby, so I waited for a while. Now it does not react, unless it plugged in to a Mac. When it is plugged in the apple logo appears for 10 seconds and then it´s gone. It has been blinking for about 4 hours now. I´ve tried to hold the power and the home buttons in several times, but it does not work. It was and still is fully charged. Anyone who has any experience with this?