Drop the battery for a few hours, and then try again on the WSOD phone. My K800i did this once, and I can't remember what I did to fix it, but I arsed about with it for a couple of hours, and it worked again.
I seem to recall I may also have been charging it.
Funny, cos I had only just got the phone, and thought it was already screwed lol. Never had the problem since.
Btw, it may be worth noting that SE phones have a coninential warranty as standard.