SOLVED
hello all,
i bought xpria u yesterday & was happy with it until yesterday. Today i wanted to plug my phone to my pc (win-xp sp3). I connected the phone to cpu by the usb cable (the same cable which is used for charging by adaptor). I got message that my hardware was not installed completely. Then I downloaded pc companion from internet & tried everything i could but the pc companion couldnt even detect my phone. I followed everything mentioned in this post. but unsucessfull. i also tried repairing by PCC. When followed the step in which i press lower volume button + insert usb i got a green light in the transparent band. Then my pc started installing drivers again but still got some error, though this time it could recognise the name 'ST25i'. In device manager i can see SEMC HSUSB Device (has a yello exclamation) under Portable Devices. 
Can anybody help me?:smileysad:
Why you did this to me Sony? I have been your loyal consumer, but now it seems you have started compromising quality & costomer satisfaction! Certainly I will NEVER buy my next smartphone from U. 
Hello,
I have the same problem but when I download and instal drive i have this massage:
i've experienced d same problem in my fone earlier it used to connect without any trouble bt one day it showed error i tried everything stated here bt no use dn i uninstalled the PCC and switched on USB debugging mode and den reset my fone settings(NOT FACTORY RESET) then i connected USB and intalled PCC via phone and it worked for me hope it works for you too 
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