So, what I mean by that is this:

In Fullscreen what the game does is it acts like it is supposed to graphically, but I can't move my mouse outside of a 720p resolution. So I can't move it right or down indefinitely, which isn't crucial, but it's extremely annoying. For example, when I just need to slightly turn to the right I my mouse stops and I have to do a 360 turn to the left.

In Windowed Borderless I have that same problem, plus any part of the screen that doesn't fit inside a 720p resolution is totally black. So that's even worse.

In Windowed mode everything is fine besides the fact that it's windowed mode. I can play like that, but it really takes a lot out of the game, seeing all my files on the desktop in the background and such. In short, this makes the game playable, but not really as fun.

In 1280x720 resolution, absolutely everything listed above is fixed, except for the fact that the game will crash every 1-3 minutes or make every single texture that doesn't belong to an entity flicker or just not exist allowing me to see through walls or host a strobe party.

I even tried turning on the "Primary Display Driver" (I think that's what it's called) but all that did was drop my framerate to a few a second and lock it that ways so no matter the graphical settings I administered it was like that, forcing me to re-install the game.

So I've looked through files, did research, scowered the forums but nothing helps. I did find one other person with the exact same problem as the first one listed in this post but that one was a year ago and never got any replies. Thanks for any help!

I run Windows 8.1 and had the same problem. I solved it by going to the game's properties (right-click the game's exe, click properties), click on the compatibility tab at top, and check "Disable display scaling on high DPI settings". Worked fine after that. Hope this helps.

I run the game on Windows 10 and it seems fine for me.
Altough using the borderless windowed mode might be better for Windows 8 and higher (I can still run Blitz3D programs fine on fullscreen, but some things are still buggy).
Or try to use the method Kreton described (I never tested it myself, but it might do the trick too).