I don't know what I can do to fix it, so I'm asking you guys.

Whenever I load up Portal 2, it, loads to the loading screens,(Before the main menu, the ones with the Co-Op bots or Chell and GLaDOS)and then it closes the program without warning, or any boxes that say "PORTAL 2.EXE IS NOT WORKING END NOW?"

This happened after I downloaded a custom map. I don't want to give his/her name away because it's probably not his/her fault.

Try verifying the game files in Steam.

WinstonSmith wrote:
Try verifying the game files in Steam.

I'll try that. Where can I verify them?

right click on the game in steam then click propeties, then click local files, verify game cache, something like that.

Spam Nugget wrote:
right click on the game in steam then click propeties, then click local files, verify game cache, something like that.

Okay. I've done that, but it's telling me to close any running games or tools before verifying them. I closed all except for Portal 2-Properties.

It can happen that a game crashes but is still stuck in memory. Also, Steam sometimes thinks a program is still running while it isn't.
Try exiting and restarting Steam. If it doesn't want to exit, restart your PC.

(Or you can end the Steam program and any "stuck" games via Windows task manager, but that's a bit more risky. Killing the wrong program can break other things on your computer.)

HMW wrote:
It can happen that a game crashes but is still stuck in memory. Also, Steam sometimes thinks a program is still running while it isn't.
Try exiting and restarting Steam. If it doesn't want to exit, restart your PC.

(Or you can end the Steam program and any "stuck" games via Windows task manager, but that's a bit more risky. Killing the wrong program can break other things on your computer.)

Oh, okay. Thanks, I can play Portal 2 now.