A: When a machine wakes from sleep, an Event Log is written to the System log, Event ID 1, with a source of Power-Troubleshooter, which tells the source of the wake-up.

In the example below, you can see it’s the MED-V Guest Wakeup scheduled task. To stop this wake-up in the future, I would modify this scheduled task to not wake the machine.

Log Name: System
Source: Microsoft-Windows-Power-Troubleshooter
Date: 10/30/2011 11:59:48 PM
Event ID: 1
Task Category: None
Level: Information
Keywords:
User: LOCAL SERVICE
Computer: savdalwks01.savilltech.net
Description:
The system has resumed from sleep.

Sleep Time: ‎2011‎-‎10‎-‎31T01:29:37.685300500Z
Wake Time: ‎2011‎-‎10‎-‎31T04:59:47.972820600Z

Wake Source: Timer - Task Scheduler will execute '\MED V Guest Wakeup - Scheduled Task - john@SAVILLTECH' task.

To see more FAQs, please go to John Savill's FAQs page on Windows IT Pro.