did you remove the pci-e card when you connect ot the onboard one you have to
No I did not but I tried reseating nearly all the components to the mobo & PSU. I'm happy to report that the monitor is working again, but I had to do the following to get to this point:
I used another VGA-input monitor I had lying around (luckily) and it was able to receive signal from the GPU (strangely, not the mobo though) even though all drivers for the GPU had been uninstalled. I was able to access the BIOS and switched the storage settings from default (IDE) to AHCI. I was amazed when I restarted, logged into my Windows profile, and found all my files and folders just as I had left them (which I didn't fully explain, but I went through an arduous and complicated process to configure symbolic links from the C:\ to the D:\ for optimal storage responsibilities - another topic entirely).
So here I am, at square one
At least I didn't have to reconfig everything. However, my initial issue may still exist: that is, receiving the error message about the display driver failing but subsequently recovering when I play a game. This issue does not come up when watching video. Anyway, thanks for the info everyone. I'll be updating the other thread (linked to in my original post) if the error message about the display driver crash persists.