To allow for Replay Media Catcher to wake your computer for scheduled recordings, you need to make sure you have enabled the option in Settings->Advanced. Additionally, you may need to adjust sleep settings on your computer. Open up Control Panle\Hardware and Sound\Power Options. Click the "Change plan settings" link next to your current power plan. In the Edit Plan Settings window, click the "Change advanced power settings" link. In the resulting Power Options window, make sure enable the Sleep->Allow wake timers.
