[ubuntu] Server stops respoding - goes to sleep(power save)?

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http://ubuntuforums.org – Hi, I have poweredge 1435SC and I just installed Ubnutu and after a while 5h+ it stops responding. The way I see it i can not SSH to it anymore, i get connection timed out. When I had debian installed I didn't have this problem, so I'm assuming there's a setting of some kind? Can someone point me to the right direction where to disable it? Thanks Server info: Welcome to Ubuntu 11.10 (GNU/Linux 3.0.0-12-server x86_64) (Hardware)