Crashing 1-2 seconds after start-up

I’ve been trying to find a way to fix this problem, but nothing seems to be working. Every time the game loads, it just shows the blue loading screen, then closes instantly, with no window popping up that explains what went wrong. I’m not very familiar with figuring out how to fix this kind of stuff, so any help would be appreciated.

Try verifying game cache integrity of Team Fortress 2 and Garry’s Mod.

as well as css

If that doesn’t fix your problem I would start removing addons