Originally Posted by till
If you dont find anything in the logs then its most likely hardware related. At 4 AM run serveral cronjobs which may cause a higher load on your server, if there is e.g. some bad RAM or power supply, the server might die.
Could be a heat problem, have a look at the cpu-cooler.
Had the same problem here, cron start >> server shut down no entry in any log.
Cpu cooler not running