you have to download :-
1. latest sony ericsson pc suite 6.0
2. sony ericsson update service (seus)

how to download????????????
go to Sony Ericsson - Home
click on support
select your mobile on left side
now at the middle of the window click on
""Software downloads Find useful software to manage your media files, update your phone software and more.""
now click on pc suite and update service to download..... thats it

now install update service software,,after installing,go to
C:\Program Files\Sony Ericsson\Update Service\setup\drivers
now extract the rar file "USBFlashDriver" thats all

now install sony ericsson pc suite 6.0
before repair your phone take backup of your mobile with pc suite
connect your phone on "phone mode"
click on "backup and restore" option,,(left pannel)
take backup,,,,
backup option will not backup your "text messages"
for that, go to "text messages" on left pannel
or use another software..


now in pc suite,,
go to the pulldown menu....go on "help" tab....and click on "phone repair"
click on continue
(your net connection must ON,,& turn off your file download manager like idm and dap,,pc suite will download latest firmware for your model, let him download it self without any download manager... )
it will take only 10 minutes to download updates
after downloading ,,pc suite will tell you to connect your phone (a message will appear with instructions ""how to connect"")
then turn off your phone ,,remove memory card ,,sim card,,
remove the battery and insert battery again but dont turn on the phone
now take your usb cable,,connect it to pc first,,
then you have to press and hold "c" button,, {{ ""cancel button"" of your phone ****
and connect usb cable to mobile holding "c" button
a message will appear "release "c" button"
after that pc suite will repair your any software problem
enjoy...