Taking Application Data backup via iTunes

All of a sudden, my iPhone 4 screen has stopped working. It means I can not turn on the screen at all. I tried calling my phone from another number, it rang but screen appears black. No way I am able to see anything on the screen.

Now I plan to hand it over to service center.

But I want to take back up of my Data from my phone first.

Is there a way to take all data backup via iTunes and then erase everything on the iPhone.

My concerns are:

1) I have personal chat n pictures on watsapp which I deleted from phone camera folder (All incoming pics auto saved to camera album), But I could still see them inside watsApp album (i.e. even after deleting from phone's camera folder). I want to take a backup via iTunes and then want to delete all the data from phone.

2) My mail accounts are open. How do I secure them before giving it to service center.

3) How do I erase everything from my phone before giving it to service guys? Even if I am not able to take any back up, I would want to delete everything from my phone.

I had disabled any cloud back up for camera or watsapp.