Click on the Mouse icon in the following directory: Control Panel\All Control Panel Items. A new window should open labeled as "Mouse Properties"; click on the "Pointer Options" tab and make sure that the "Display Pointer Trails" options is unchecked.
Special Note for those affected only on Dominion:
Make sure that under "Mouse Properties" that "Hide Pointer While Typing" is unchecked in the "Pointer Options" tab.
Key Strokes Not Being Detected
This is often caused by a failure in the input.ini files, causing your keybinds to not be saved. Resetting your bound keys by deleting the input.ini file and letting the patch re-add the file with default key assignments is the most effective way to fix this issue.
Steps for resetting your input.ini file:
While in a game, most preferably a Custom Game, press 'ESC' to open the in-game options
Click on the option for 'Key Bindings'
Change any binding that is in the list of changeable options and save the changes.
Completely exit the game and navigate to the following directory:
C:\Riot Games\League of Legends\Config
Delete the newly created input.ini file and relaunch League of Legends
Once open the game should repatch and restore a default input.ini file
Q, W, E, R Appear as Numbers while Binding
This issue is caused by conflicting software or another application. Password encrypting software is most often the root of this problem. If you are knowledgeable on the exact application that is causing this, uninstalling the program is highly advised and should solve the issue. Ex. Comcast Constant Guard.
If you are unsure of the application that is causing this issue, please send in a support ticket with a process list attached so that we may best assist you in identifying the application that may be the root of the problem. A detailed guide to doing this is provided here:
Some key strokes and mouse functions are not available to be directly modified through our in-game options. This may be particularly difficult to deal with as a left handed user or a player that owns a mouse with more than 5 buttons.
Setting Your Mouse Up For Left Handed Use
Some of our users have asked for the ability to switch their left and right click for better use when playing with the mouse in their left hand. Although, this option cannot be altered in game, it can still be done by editing the input.ini file. We have attached the necessary file at the bottom of this article.
Once you have downloaded the file it should be placed here: C:\Riot Games\League of Legends\Config
Extra Mouse Button Binds Not Working
At this time mouse buttons beyond 'Mouse 5' are not detected by our game and cannot be bound through the in-game options or by adjusting the input.ini file. If you have a mouse with these options you most likely have a product from Razer, Microsoft, Logitec, etc. These commonly come with separate drivers either on CD or easily available on their respective support sites.
Once you have downloaded these drivers, open the options that allow you to reassign mouse keys to any bind of your choosing. We highly suggest that you choose buttons that are not being used in game or assign them to the same key that you originally wanted to replace.
Logitech Keyboard and mouse
If you are using Logitech Keyboard and/or mouse please take a look at this article.