Our Vista Media Center machine was continually waking up a few minutes after it was put to sleep. This lead to higher power bills, and higher greenhouse gas emissions. To find out the cause of the last wakeup request, you can execute the following command from a Command Prompt:

powercfg /lastwake

Unfortunately, this didn't give any useful information for me, so I took the following approach:

  1. Identify the devices that can wake the machine up: powercfg /devicequery wake_armed
  2. Disable any devices that do you not explicitly want t o wake to machine (such as the eHome IR receiver): powercfg /devicedisablewake "device name here in double quotes"

Now, you should be able to put the machine to sleep using the remote, and it will only wake up for scheduled jobs, such as recording your TV shows.