[xubuntu] Toshiba laptop in dual boot restarts after shutting down Xubuntu

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http://ubuntuforums.org – Hello, I bought a new Toshiba Satellite C870-15J with Windows 7 installed. Made a dual boot with Xubuntu 12.04. When I shut down Xubuntu, the system seems to turn itself completely off, but after some seconds I hear a click, and the system reboots itself. The same when I shut down via the terminal with "sudo shutdown -h now". In the power manager I changed the value for the onn-off button to shut off, but still the same problem. I also entered the bios and made sure every Wake-on-LAN-like-function is disabled. In grub I changed GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" to G (Hardware)