How do I connect Lenovo Thinkpad 450s to External Monitor

A customer recently brought in the Lenovo Thinkpad T450s because the screen was failing.
When I hook up the new screen, there's no display at all.
And so I connected an external monitor through the VGA Port ( To boot the system into safemode to try to reinstall the display driver ), however the external monitor only displays a black screen and the mouse cursor and nothing more.
Any thoughts on the issue?

The fn+f7 combo is supposed to switch your display to external, but without being able to access the desktop due to the laptop screen display issue, it won't allow me to switch.

Caleb

That is perfectly normal. A bootable Windows OS from the hard disk loads the default simple VGA level driver. That driver supports only low resolution and no external monitors. Once you get past the sign in, the complex video driver loads to support advanced display settings.
Booting to safe mode will get you to a more complex driver that has the cursor on a second screen, but no desktop wallpaper there. No icons either, no safe mode utility screens, no way to tell what you must do to make the external screen the primary one. You are out of luck until you put in a replacement internal LCD panel into the laptop.
If a Windows 10 system and can boot normally past the password sign in, and can get to the invisible desktop, a "Windows" key and the "P" key will get to the drop down menu to make a display change. 3 hits of down arrow and Enter will get you to second screen only.

Starrysky