(See the best response by Lummox JR.)
I've attempted clearing all the directories after uninstalling, switching to the beta client, using task manager to close BYOND. I am able to compile .dme files, host servers (which my friends can join!!!) but I'm still unable to boot the Pager.

I am running Windows 10.
Best response
This sounds like the window position is wrong. Go to your BYOND user data folder (usually Documents\BYOND), open cfg, then open pager.txt and delete the window-pos line.

Before you do this, make sure byond.exe is not running in the Task Manager.
In response to Lummox JR
That fixed it. Thanks.