I opened up a file of mine in TexWorks. There were no line numbers. So, I navigated to
Edit > Preferences and checked the line numbers box.
Oddly enough, if I open up a new empty document, line numbers are displayed for the new document. However, there are no line numbers in my existing document. I have tried closing TexWorks, restarting it, and reopening my document. However, anytime I open my document instead of creating a new one, line numbers fail to display.
I'm running Windows 10 Home Edition