Apparently some "fmod.dll" file is missing from my computer, and SCP Containment Breach won't run at all.
I tried reinstalling already, to no avail.

Is "fmod.dll" inside the game's directory?

Yes, it is downloaded with the game. For some reason it doesn't seem to want to work though. I'm still a bit shady with how these things work, so I've just followed some steps on YouTube. (Yes, I DID go to the actual website. I wasn't led to a virus)