typedef enum 
{
         PowerActionNone = 0,
         PowerActionReserved = 1,
         PowerActionSleep = 2,
         PowerActionHibernate = 3,
         PowerActionShutdown = 4,
         PowerActionShutdownReset = 5,
         PowerActionShutdownOff = 6,
         PowerActionWarmEject = 7
} POWER_ACTION;

Windows Vista Kernel Structures