I can't restart my iphone 5Se, connected to a pc with itunes and no change. What can I do now?

Connect your phone to pc then Press and hold the Sleep/Wake button and the Volume Down button until the screen turns off. Continue holding the Sleep/Wake button + Volume Down button, even after you see the Apple logo appear. Then

Release the Sleep/Wake + Volume Down button once you see the Connect to iTunes message appear on the iPhone.

Launch iTunes and you should see a message stating that There is a problem with the iPhone that requires it to be updated or restored.