I know there was a thread on this some time ago. I am just stumbling into the issue on a Gigabyte GA-P45-UD3P MB. I have set up a task in Task Scheduler to wake up the system and hopefully stay awake until another shutdown task is initiated via Task Scheduler. I have the power options set to Never/Never. When the wakeup task runs at the appointed time the computer wakes up (the monitor stays blank but that's ok) and then goes back to sleep in 120 seconds. I guess that is a feature of Window 7? Anyway, can someone please tell me what the heck I have to change (in the registry?) to get this thing to stay awake until I tell it go go back to sleep. Thanks.
Found the answer to may problem. Sleep Return Timeout for Unattended Wake Up