It's likely that you need to reflash the phone software to your phone. You can do this yourself [detailed instructions and files at se-nse.net] or just do it at a phone shop or through an online site like Da Vinci or Wontan.

But something you should try is to remove the battery and take out your SIM / memory card and then let it sit for a bit before you reinsert the battery [withouth SIM / memory card] and restart the phone. Hopefully that'll work, if not then you'll probably have to reflash the phone software. But you could always check by doing a software upgrade using SEUS [Sony Ericsson Update Service offered for free here - http://www.sonyericsson.com/cws/support/...