Blocked components, piled up on the left - Android Studio

When adding components to the design, they appear stacked in a pixel in the upper left corner and can not be moved or resized. I already tried several ways to fix it that they suggested in other publications and reinstalling after deleting the folder "C: \ Users .... AndroidStudio3.1" but it did not work. Any ideas? Thanks.

<?xml version="1.0" encoding="utf-8"?>

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Hello World!"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

In the .xml mark me this: xmlns: app="http://schemas.android.com/apk/res-auto" is not being used.