Hi
I don't know about the white screen, but my K750i went through a period of resetting itself, or simply switching itself off.
I worked out it could be one of two things.
(1) I used to charge the phone in the car a lot. I stopped doing it as much, and only charge itif I am running really low on battery. Even then, I will charge up on the mains when I get back home/to the office. (I had a similar problem with a T630 which I only got charged in the car cradle, and was for over resetting itself. I went throught 3 T630s, all of which had the same problem. When I got my K750i, I gave the T630 to my wife who only charges it on the mains and has never had the problem).
(2) I also wondered whether the battery was lose. I put a bit of folded paper into the battery compartment to hold the battery in more firmly.
I can't remember the last time the phone reset itself now. As I did both actions at the same time I never worked out whicj one was the solution.
kfv