The client may suddenly disappear after you log in. Usually, this is due to an authentication error or other miscommunication with your computer. To fix it, follow these steps:

Run the game as an administrator

  • Right-click on your League of Legends shortcut
  • Select Properties
  • Check the box labeled “Run as Administrator” under the Compatibility tab
  • Note: If you’re using Windows XP, you’ll need to log in as an Administrator instead

Sync your Windows clock

  • Right-click on your computer's clock and choose "Adjust date/time"
  • Select the Internet Time tab and click the "Change settings" button
  • At this point you may receive a UAC prompt. After this prompt, click the "Update now" button to resync

Temporarily disable your firewall

If you’ve installed a third-party firewall, try disabling them before logging in. Windows comes with its own firewall, which you can disable by following these steps:

  • Click on Start
  • Click on Control Panel
  • Click on System and Security
  • Click on Windows Firewall
  • Click on “Turn Windows Firewall on or off” (you may be prompted to enter the Admin password at this step)
  • Under each network location, select the “Turn off Windows Firewall” option