It shouldn't be rebooting, that is not normal beyhaviour. My N800 and N810 stay switched on permanently and they've never rebooted on their own in all the months I've had them.

Something is obviously causing your tablet to behave abnormally. This is either a hardware problem, or some setting or installed app is causing it.

To find out which one of these it is, back up your data and flash the tablet with new firmware. You can see a step-by-step guide to how to do this here:

http://tabletschool.blogspot.com/200...-firmware.html

After you've updated the firmware, do NOT restore the backup yet. We want to keep the tablet "clean" so we can find out whether it's a hardware problem.

Connect the "clean" tablet to your wi-fi, and see if it reboots overnight.

If it doesn't reboot, try installing Skype and leave it connected overnight.

If it still doesn't reboot, try restoring the backup you made, and leave it connected overnight.

If it reboots after restoring the backup, then it's likely that your settings or installed applications are causing the reboot. You could re-flash the tablet firmware again and then install your apps one at a time if you want to find out which one, or there may be some cleverer way of doing it which someone may tell us about in this thread. :-)

If it reboots when the tablet is still "clean", then it's likely that your tablet hardware has a problem and you may need to get Nokia to repair or replace it under their 1 year hardware guarantee.