connection problem

I have a connection problem. Who can help? I've already reinstalled the game 3 times, and it's currently being installed for the fourth time. The problem is that during the game, I suddenly return to the menu, and an error message appears indicating a connection issue, even though my internet connection is stable. I have to restart the game, sometimes twice. If anyone knows a solution, please let me know. (Additionally, I am unable to play Portal. When I connect, I am immediately returned to the menu.)