i have similar problem from several days with my phone.I trying with;
*cold flashing
*resize partitions
*change 2 bat.
*advice from xman did not help me(by the way big thanks to freemangordon for everything)
*flasnig few times under linux
*from x-trrminal with commands reboot -d 0 and poweroof -d 0
*install droid and from power menu i puch reboot and shutdown

Finally i changed the board from my second phone(damage usb port) and voila the phone has been fixed.So if we have anything different from what i am done,please tell me.
regards
note:i forgot to mention when display turn off or i lock the phone,immediately follows reboot,olso i tryng with syslog(start sysklogd under root)but nothing happen,the reboot continue