Garrys Mod turning my screen sideways. Please Help!

I just bought this game along with counterstrike source, and when I open either game, they turn my computer screen sideways along with my mouse cursor. Garrys Mod also goes completely black when my startup menu is loaded, All I can see is my sideways mouse curse. I’ve tried reinstalling it, verifying it, defragmenting it, customizing launch options and ect…

(User was banned for this post ("Use the Help & Support section" - Orkel))

As a temporary solution, you could place your monitor on its side.