Hi Gator,
We are glad to assist you with the issue on Microsoft Community.
Before I approach towards any suggestion, I would like to collect some information on thsis issue:
Are you referring to the Local screen on the computer?
If you are referring to Lock screen on the computer, then let us try the following steps by navigating to “Change PC settings” on the computer.
Please follow the steps:
a) Press Windows and c key together to open the Charms bar.
b) Click on Settings.
c) Click on Change PC settings option at the bottom of the charms bar.
d) Click on Personalize option.
e) Click on Lock Screen.
f) Choose the required picture you want to save as the lock screen picture.
You may refer to the link below in response to this query:
http://windows.microsoft.com/en-US/windows-8/change-backgrounds-pictures#1TC=t1
Hope it helps. Please write us if it does not resolves the query.