Hibernate and automatic shut down after idle at login

Hi there,

I'm using hibernation on one of my PCs. When I power on the machine
and the system is resuming state and is ready to use and I don't login
on the terminal for about 4-5min, the system automatically shuts down
and goes back in hibernation. As soon as I login one time, the systems
stay up and running -even when I log off.

How can I disable this behaviour?

Thanks for hints.