Hi @TomVreklo, I am sorry to hear about this.
I am afraid that it is quite hard to say whether this is caused by the software in the phone or if it is the hardware that is malfunctioning from a distance.
The first thing that i would suggest that you do is to try to perform a software repair using a computer and Xperia Companion. Please note though that a software repair will erase all user data, so remember to do a backup of your user data first.
If you have performed a software repair and the lines on the display remains as before the repair I suggest that you get in contact with your local support team in order to have the phone sent to an authorized service center. If you have any questions regarding the service, such as routines, warranty and consumer laws, these type of questions are best answered by your local support team as well, as they vary between markets.
Try this and let me know how it goes!
