Have you got a black screen or are you stuck on the white screen with the sony logo?
yesterday I was stuck on the white screen and it wouldnt go any further, I had to connect it to the xperia companion for a software repair which fixed it.
Btw, the power and volume, its the volume up key and you have to press together for at least 10 seconds until it vibraes once and then three times. However this only worked with me whist I was stuck on the white screen.
This seems to be a coomon problem with the xperias. I hope you manage to fix it.
