suddenly my laptop did not suspend when i closed the lid. i checked all settings of my linux mint 17 installation and all settings where correct. a quick search pointed me to http://askubuntu.com/questions/395428/laptop-does-not-suspend-when-lid-is-closed.
the solution for me was to edit
/etc/systemd/logind.conf, changing the option
suspend (valid options are
poweroff) and reboot the machine.