Why wont Team Fortress 2 fully load?

I downloaded the now free game and everything is going well. I went to practice and tutorial levels and it loaded them well and i played with the bots. Then when i go and choose a server to join to play with actual people it goes to the loading screen loads till there's about 4 bars left and stops there. Ill just keep it there and eventually it'll just go back to the main menu. Any ideas as to why it does this to play online only, and not with bots?