After hitting the launch button nothing would happen so I tried relaunching it, but it said it was already running and a black box appeared at the upper left hand corner of my screen. I could minimize and restore it, but nothing happened. I had to restart my computer to exit the application (when I used task manager to close it and tried relaunching it said it was already running). Running it on Windows Vista 64-bit if that helps.
same issue here. 
Same issue as well. Windows 10 here.
I press the button and nothing happens. I open the client again, says another instance is running and it just shows a dark blue/black square after that.
It's a problem with the launcher. If you go to your installation folder of LoL and open LeagueClient.exe directly there is no problem.
Same problem here. I tried the leagueclient.exe work around, same problem happened.
Edit: nevermind. I clicked the wrong the thing. The leagueclient.exe work around does work.
The real question is why the fuck you are still using Windows vista
same problem here, if i launch lolclient.exe it shows me directly the darkblue screen
I had the problem too (got a blue square in the corner in the corner, file wouldn't open, tried going to installation folder, etc.). Managed to get it to work by going to task manager, closing the application if there is one. Then went to the processes in the next tab of task manager and ended the LeagueClient process. After that, right click league --> properties --> Open file location --> LeagueClient (the one with the new updated "L" symbol). Hope this helps!
same here..
yea same here.
