Player Support Specialist
Thank you for bringing this to the Help and Support Forum! If you receive a "application has failed to start" error, and you have already attempted to re-install, it may suggest some problems with the configuration of your system permissions. League of Legends requires administrative privileges to install and run correctly. There are several common fixes for this problem I would like you to try:
1) Make sure you have the most recent Windows Updates
2) Ensure that you are an Administrator
3) Attempt to run League of Legends as an Administrator by right clicking the short-cut, selecting properties and checking the box saying "run as administrator"
Keep in mind that these are only some of the more common resolutions for an issue such as this. If these solutions did not fully resolve your issue, i strongly suggest submitting a Support Ticket so we can work with you one-on-one until a resolution is found!*
* Keep in mind that this advice was given based upon the information provided. If you would appreciate a further one-on-one interaction to solve this issue, make sure to send us a Support Ticket! You can send one from here: https://support.leagueoflegends.com/tickets/new Also, if you could please provide a link to this forum thread in the new ticket, it would be incredibly helpful!