I don't think that there is a problem if XP opens File Transfer, you can click Unlock on Seking and it should read the phone, if not then you can post that it is not reading in phone....You can also try removing all drivers for W910 and then reinstalling the ones downloaded from this link
http://ma3.extranet.sonyericsson.com/drivers/. If again doesn't work then go through steps in this
tutorial to remove all W910 related drivers that you see washed out (previously you should disconnect phone) in Device Manager.
BR