There is a known issue with layout and menu items in Retail Pro.
This issue is often presented by a blank page with no Interface available.
EXAMPLE
To correct this issue, you must go to into your Windows File Directory on your taskbar.
Example
From here, we have one of two options. We can go to Local Disk (C:) - Then to the "Retail Pro9" Folder - and lastly to the "Layouts" folder.
Alternately you can copy and paste the below address into the text bar at the top of your Windows File Directory.
C:\RetailPro9\Layouts
Once inside the Layouts folder, locate your username.
From here, we have one of two options. We can copy the files within another user folder into yours, the benefits of this being that their layout may be similar to yours.
Alternately, the defaults can be restored by unzipping and copying the contents of the "sysadmin" archive folder located at the bottom of this article.
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Preventative Advice
To prevent the loss of your preferred layout, best practice is to make a copy of your layout folder (when working), and place it in a secure folder for use if this scenario occurs again.