If after logging in or adjusting your screen size you experience the following,  it simply means that your software window is too big/small for your screen

A full Black or Grey screen

A screen with a stripe of grey down the middle

A very small screen

This one is an easy fix as just by using Alt + Enter your screen will become adjusted and the log in window will appear

Example of possible incorrect view. 

If after resizing you wish to change the resolution please use this Help Guide Using the Correct Resolution