Ozcar Ellenius :
I have the same problem and my phone was bought without sim carrierfree
My friend, it happened with me and in my case I am sure it was caused by water even with the covers closed properly the water goes where it shoud not go. After my phone died I put It to charge and the sony logo appeared and started to charge normaly but when i tried to turn it on the phone would vibrate 3 times and start all over again on the charging screen.
The only solution was to use a hair dryer, First step: take your sim card and memory card out of the device sou the air can circulate better. Now use the hair dryer in the hot mode, becareful not to damage getting it too close to the phone but know that it should get hot enough to vaporize the water inside so it has to get a high temperature.
Move the hair dryer heating all sides of the phone and inside where you opened the covers. I had to do it for a long time to make it work again. the phone is working fine now, just as it was before.
Dont believe sony about been waterproof, it can become an expensive nightmare, only use in water if you really need, many people are having problem even with covers well closed and if you still do it, make sure you don´t press the power or volume buttons under water.
I hope it works for you!!