Hello Mary,
Thank you for posting your question on Microsoft community.
I would like to know some information about the issue so that we could help you better.
Are you trying to use split screen feature(Snap)?
You can use Snap to arrange windows side by side, which can be especially helpful when comparing two documents or when moving files from one place to another.
Please refer suggestions from Lead3 replied on December 27, 2011 and check if it helps.
Please also use steps provided in this article and check.
Refer:
Arrange windows side by side on the desktop using Snap
http://windows.microsoft.com/en-US/windows7/Arrange-windows-side-by-side-on-the-desktop-using-Snap
I hope this information helps.
Please do let us know if you need any further assistance.
Thank you