I changed my hz to 200 and now it says I cannot display this video mode even when I start up sc2. Is there a way to reset all settings without starting up the game or something?
If you changed it in StarCraft 2, open your Variables.txt file (which can be found in C:\Users\{YourUserName}\Documents\StarCraft II). Search for the line "refreshrate=" and delete it, or set the value to 60. I would recommend finding your monitors drivers. If you are unsure where to look, most your monitors make and model here and I will track it down for you. If this ever happens to you again, just wait 15 seconds after setting a value like that, and the screen will revert to normal (yes, even in StarCraft II.. its setup to do that).