I had the same problem with the random blackout and as soon as I lock and unlock the display goes on. However my phone took a dive in lake for 30 seconds.

http://talk.maemo.org/showthread.php...013#post710013

I tried the rice trick and after it was dried the problems started. The I tried re-flashing and so did the people in the Nokia service center. The problems did not go away and the second time they replaced the whole slider mechanism. That also did not fix the problem so they eventually replaced the phone for a new one.