To get Chrome back to filling the screen normally, press the Windows key and the up arrow together.
Then, to get rid of the 'half page' problem, clear Chrome's cache:
https://support.google.com/accounts/answer/32050
To set Google as your home page in Internet Explorer, go to
https://www.google.co.uk/
Click on the cogwheel.
Select 'Internet Options'.
If it's not already pre-selected, click on the 'General' tab.
Under 'Home Page', select 'Use Current'.
Click 'Apply'.
Click 'OK'.