I had the exact same problem yesterday. Pulled my 8900 out of my pocket and found a white screen with the clock. Pushing various buttons didn't work, so I tried a battery pull. After reinserting the battery, the red light would come on for about five seconds and then right back to the white screen and clock. Tried about five battery pulls and even waited about ten minutes before reinserting battery but same results.
After searching the forum and figuring I had to go out and get a new phone, in a final act of desperation, I started pressing all the buttons on the keypad (angrily, I might add). Somehow that did the trick and the phone slowly came back to normal. I don't know how this fixed it, but it did. It could be just luck.
I re-synced it and it seems to be working fine. Before pressing all the buttons, I did check in the very beginning if there were any stuck buttons that might be causing the white screen, but I don't think any were.