Nowadays this is a common known issue with a Nokia N810 tablet. I encountered it 5 months ago - sometimes it restarted 1-3 times a day, sometimes 1-2 times a week, and sometimes worked pretty well without this problem. I reflashed it several times - it worked week or more without problem, I didn't install another applications, but in spite of this the issue came again.((((( There is a Bugzilla post with a known issue called BUG 3415 / you can visit it too - here is the link: https://bugs.maemo.org/show_bug.cgi?id=3415