A program or scheduled task might be waking your computer. By default, Power Option settings do not allow scheduled tasks to wake the computer from sleep or hibernate. However, some programs might awaken the computer if these settings have been changed.
To prevent programs from waking your computer
1. Open Power Options by clicking the Start button , clicking Control Panel, clicking System and Security, and then clicking Power Options.
2. On the Select a power plan page, click Change plan settings for the plan that you want to change.
3. On the Change settings for the plan page, click Change advanced power settings.
4. On the Advanced settings tab, expand Sleep, expand Allow wake timers, choose Disable for both when your computer is running on battery and when it's plugged in, and then click OK.