How do I reboot a CRASHED system via network? [closed]

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http://stackoverflow.com – We have a linux machine in our lab that is used for experimental purposes. And, every now and then, it crashes, and we can no longer log-in. So, we find ourselves having to manually push the restart button. Is there a way to reboot a crashed linux system remotely? Note: Doing this over the LAN would be the optimum solution. Otherwise, an affordable device that responds to network commands, and does an off/on to the power source directly would be good too. Thanx! (HowTos)