//somewhere in the init
orxMath_InitRandom((orxS32)orxSystem_GetRealTime()); //a good seeding value

This also will ensure your random values from your Data Config are also properly randomised. See also Spawning Random Objects as a practical example of using random values.

//elsewhere, a random number between 1 and 100
orxFLOAT randomNumber = orxMath_GetRandomFloat(1, 100);