Don't panic, go step by step.

• restart your device
• use the Support App where solutions to common problems are presented

Problem still there?

• restart your device in safe mode and see if the problem is still there
  • in safe mode your device starts with just the pre-installed apps loaded
• Have a look at the Xperia support channel on youtube 
• Search the forum
• Ask on the forum
• Contact Sony support through the Support App on your phone
  • by chat
  • by phone
  • by mail

The support app is great for help and finding the possibilities of your device.