If the phone is "soft-bricked" or the button combinations aren't working, you can use the Xperia Companion (formerly PC Companion) on a Windows computer. How Do I Factory Reset with PC Companion? - Community
: While holding those two buttons, briefly press and release the Power button . sony ericsson mt11i hard reset
: Press and hold the Left and Right buttons located directly beneath the display. If the phone is "soft-bricked" or the button
: Continue holding the buttons until a menu or instructions appear on the screen. Follow the on-screen prompts to confirm the "Wipe Data/Factory Reset". Method 2: Reset via Secret Dialer Code : Press and hold the Left and Right
Choose and confirm by tapping Reset customization and reboot . The phone will restart and begin the formatting process. Method 3: Reset Using Sony PC Companion (Official Tool)