The Linux Help and Tutorial Thread

[D_A]

Hunting through the Ubuntu forums I came across someone with a similar problem. In their case it ended up being an incompatibility between the new ACPI and their BIOS and flashing to the latest BIOS update solved it.
Just a thought, but is the system set to turn off your monitor or anything like that after an hour?

edit: it also appears that XBMC has a setting that does exactly this.
In the System settings there's an option called "Shutdown function" and "Shutdown function timer". I'd be suspicious they may have something to do with this.