Plutonium

When I try to play solo zombies, instead of the normal screen popping up when I click SOLO, it's a blue and grey checker texture. I verified the integrity of game files on Steam and two files needed to be validated. So then I tried playing on Plutonium again but then the same thing happened. When I moved my mouse around to try to find the button for the desired level somewhere and click it, there is no loading screen, it's just a black screen that seems to last forever.