Not entirely sure what's going on there.
First thing I'd try is going into the %APPDATA%\obs-studio directory with OBS closed, and rename the 'basic' subdirectory something else (like basic_bad or something) then try starting OBS again.
OBS' settings are stored in that 'basic' folder, not the main install directory, so uninstalling/reinstalling the program isn't going to help anything, with the settings not being touched. Doing the above will remove your settings and generate a fresh default set, which (probably) will fix whatever's going on. But it WILL reset everything in OBS to defaults... not really a problem if you're just getting started.
Alternately, there's the possibility that OBS was moved offscreen somehow. You could try starting OBS, waiting for it to 'vanish', then hitting CTRL+Space, M, press the arrow keys on your keyboard, then wiggle the mouse a bit. This is the Windows 'move' hotkey combo (I've always had to use the arrow keys before the window would 'stick' to my mouse pointer). If it's not just offscreen this won't do anything. But if it is, you should be able to move the mouse back on-screen and drop the window on a visible spot.
DO be aware that certain programs (like MSI Afterburner!) are known to conflict with OBS, and in some cases need to be fully uninstalled. But normally those result in a crash-on-startup.