My laptop wakes up automatically exactly 12 hours after it was put into a sleep mode. It has this behavior from the beginning, it is very annoying, especially then the lid is closed and it wakes up unattended and overheats. It has Windows 7 Home Basic, runs from an outlet. Windows Event Log shows "Power-Troubleshooter" events, but specifies the cause of the wake up as "Unknown". In the Command prompt "powercfg -lastwake" does not provide any information either. Wake up timers are disabled. Wireless LAN is disabled, LAN card is not allowed to wake the computer. Neither scheduled task is allowed to wake up the laptop. Laptop is Dell Inspiron N5010.
How can I stop this behavior?