Alright, figured it out.
I'm guessing, that I probably set my external monitor to deactivate before unplugging it. The next time I plugged it in, it wouldn't activate at all for this reason.
I solved this by switching the way it got input from my laptop, going from DisplayPort to HDMI. Then I reactivated the monitor, and was able to switch back to DisplayPort.
In my personal opinion, this is truly the most idiotic thing I have dealt with so far in Windows 8. Hopefully display options such as "deactivate" don't stick around after unplugging them in the next iteration of Windows.
It happened again. Did some more research and the solution here worked:
ASUS PB278Q 1440P MONITOR "DISPLAY-PORT: NO SIGNAL, AND HDMI: NO SIGNAL" GTX 780
There is a feature on newer motherboards in which they have sleep state settings outside the control of the operating system. Go into your bios and go to APM configuration. Look for ErP setting (default is usually disabled) and enable it to S4+S5 sleep state. This solved my problem, now my monitor will show a display after computer wakes up from sleep or when powered off.