If you’re seeing An unknown DirectX error has occurred and League of Legends cannot start message, you’re not alone. Many Windows 10 users are reporting about this problem as well. At times, you might see the error instead:
No worries, it’s actually a pretty easy problem to fix. Here is one of the most effective method you can try to fix this problem.
Note: The screen shots are shown in Windows 10, but all fixes apply to Windows 7 and Windows 8 as well.
1) On your keyboard, press the Windows logo key 
and R at the same time. Type devmgmt.msc and press Enter.
2) Expand Display adapters. Double-click your display driver
3) In the Driver tab, click Update Driver….
4) Click Search automatically for updated driver software.
5) Right-click the League of Legends icon on your desktop and click Open file location.
6) Go to Config folder. Delete game.cfg and input files. The files will be restored in the next steps.
7) Go back to the League of Legends folder, then go to RADS folder. Delete lol_game_client folders (You might see two or three of them).
8) Open your League of Legends. In the game interface, click the ? icon on the top right corner.
9) Click Repair.
10) Go to Device Manager again. Right-click your display driver and click Disable.
11) Right-click the display driver again and clicke Enable.
Your problem should be fixed by now.
The steps above may resolve it, but if they don’t, or you’re not confident playing around with drivers manually, you can do it automatically with Driver Easy.
Driver Easy will automatically recognize your system and find the correct drivers for it. You don’t need to know exactly what system your computer is running, you don’t need to risk downloading and installing the wrong driver, and you don’t need to worry about making a mistake when installing.
You can update your drivers automatically with either the FREE or the Pro version of Driver Easy. But with the Pro version it takes just 2 clicks (and you get full support and a 30-day money back guarantee):
1) Download and install Driver Easy.
2) Run Driver Easy and click the Scan Now button. Driver Easy will then scan your computer and detect any problem drivers.
3) Click the Update button next to the flagged graphics dvice to automatically download and install the correct version of this driver (you can do this with the FREE version).
Or click Update All to automatically download and install the correct version of all the drivers that are missing or out of date on your system (this requires the Pro version – you’ll be prompted to upgrade when you click Update All).
