Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

You mentioned that your brother's account can log in. Is this on the same PC and connection as your account, or a different one? At what point do you get disconnected (immediately after you log in, after selecting your character, etc.)?

You only listed a few things we normally suggest, so I will add the others below.

-Reset your router by turning it off for a few minutes, then back on
-Make sure to use a wired Ethernet connection as opposed to wireless
-Check that your anti-virus/firewall has the appropriate exceptions for Final Fantasy XIV
-Perform a clean boot. Simply open the task manager and select the 'Start up' Tab. Disable everything here and restart the PC. This will make sure that no background processes are interfering with the game.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!