have you tried to change your power options in the hibernation or sleep mode, I think I have my Build 7048 x64 set to trip after 20 minutes and it does just that but I have another issue.
you or anyone else that is reading this might be able to help with my issue. It is like I said before it will go into hibernation after 20 minutes and then wake up for 20 then go to sleep for 20 and so on and so on.
The other thing to this is that it won't wake up from the keyboard or mouse, but it will wake up by pushing the on/off power switch, needless to say it did not do this with the Windows XP version.
To get back to your issue it might be in your power settings, try it.