Hmm...assuming this doesn't just happen when you're using the Internet, my first guess is that the unit is overheating especially if it won't reboot straight away.
I'm guessing that the disconnection message is a sign of the motherboard running into trouble due to the heat and since the network connection will be built-in, this fails just before the rest of the computer goes down.
It's also possible there could be a battery problem such as overheating as this would also likely cause the reboot failure. Does this happen when it's been left on for a few hours, or just after random amounts of time...?
Unless someone can bring up a magical answer, I would suspect the unit it going to need to go back to the manufacturer as laptops are really tricky things to fix.