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At first as i restart my Xperia Mini Pro, normally the Sony Ericsson logo shows on start up but right after the animation the screen hangs!!!
Need help 
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take the battery SIM and sd card out, press and hold the power button for few seconds -> only place the battery back on and try to turn it back on
if it doesn't you can repair your phone with Update Service but it will delete sms, mms, call logs, apps, settings and contacts
Update Service (SEUS)
http://dl-www.sonyericsson.com/cws/download/1/110/61/1309763183/Update_Service_Setup-2.11.7.13.exe
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Oh man your a savior. Thank you soo much and its now working. Is it a normal problem for Mini Pro? Its so annoying 
You can always use Flashtool
Xperia Mini Pro 2.3.4 (4.0.2.A.0.42)
http://talk.sonyericsson.com/message/120194#120194
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for future reference
Make sure you backup everything
Settings -> privacy -> Back up my data and Automatic restore should be selected
and also
Use one of these links to download the
Backup & Restore app
http://forum.xda-developers.com/showthread.php?t=1193802
or
http://www.elita-clan.com/downloads/backup_and_restore_v010935.apk
http://www.elita-clan.com/downloads/backup_and_restore_v010935.apkor
http://www.mediafire.com/?1n07llajeaoo03y
How to install it
You need to
go to settings -> applications -> check unknown sources
download IO File Manager
https://market.android.com/details?id=org.openintents.filemanager&feature=search_result
download the backup & restore app, transfer it to your SD card, use OI file manager to find it -> tap on it -> install it
Contacts
just to play it safe sync your contacts w/ google if you haven't already
open your phonebook
press MENU button -> tap on Send Contacts -> select all -> send it to your email
on your computer
-> download the file -> go to your gmail -> click on contacts -> click on more actions -> on the drop down menu click on "import" -> choose the file -> and click import
Apps
Don't worry so much about backing up your apps
on your computer go to
market.android.com -> log in -> click on My Library -> and send all your apps to your phone
SMS/MMS
if you don't want to use the backup & restore app then
Install "backup SMS" to back up your SMS and MMS to your Gmail
https://market.android.com/details?id=com.zegoggles.smssync&feature=search_result
or your SMS use
"backup & restore SMS"
https://market.android.com/details?id=com.riteshsahu.SMSBackupRestore&feature=search_result
or for your MMS use "Save MMS"
https://market.android.com/details?id=com.schwimmer.android.mmsextract&feature=search_result
Call Logs
And for call logs this is great
https://market.android.com/details?id=com.yang.android.ansta
it shouldn't be an issue, maybe there was a bug with the last update but I'm glad its fixed now
Amm oh wait. When i entered my sim card it hangs again sir. Awww! 
ok, so the issue is the SIM card, its probably faulty or its too old or it just stopped working, to be certain, can you borrow another SIM card to test it
I just bought another sim but nothing good happens. Luckily when i turned back my old sim the phone works. Do u think i do need to update my phone using SEUS. I have this build number 4.0.2.A.0.58 ?