This Same thing used to happen to me but do not fear, I have a solution! To fix this problem, there are a couple things you can do
Number 1: Sometimes files become corrupt during the patching process, usually due to connection issues. Forcing a re-patch should help resolve the issue. Although this never worked for me but its worth stating.
Step 1: Go to your Riot Games folder (Default path: C:/Riot Games/League of Legends)
Step 2: Open C:\Riot Games\League of Legends\RADS\projects\lol_air_client\releases{highest version number}
Step 3: Delete the following files: -releasemanifest - S_OK
Step 4: Open the Deploy folder, Delete the following folders/files:
- lib (folder)
- META-INF (folder)
- mod (folder)
- lolclient.exe (file)
- lolclient.swf (file)
- locale.properties (file)
Step 5: Restart League of Legends
Number 2: If that didn't help this is almost a guaranteed fix but u will require some things. If you switch to a hard wire connection, this should resolve any problems you have, that's what i did now lol is working fine.
Number 3: Now If you cant switch to a hard wire connection, this is fix is also highly probable to fix league of legends but may take a while
Step 1: Right click on your League of Legends shortcut and click open file location.
Step 2: Next click Riot Games on the up most part of the window
Step 3: Delete the League of Legends folder
Step 4: Re-install League of Legends
Step 5: Launch League of Legends and let it re-patch everything this can take up to 3 hours if your computer or laptop is slow.
OK i hope this helps, if you need anything else i will be monitoring this thread also plz tell me how it went.