I have the same problem with my w910i, my phone jammed zo i pulled out the battery to shut if off, and sinds then all my apps & games are gone and my Walkphone button didn't work.

What i did was update the firmware with Sony Ericsson Update Service and after that the Walkman button started to work again, as well as the media player and stuff. But i still don't have my apps + games back. But well, though life haha.