Circadian rhythm maintains sleep-wake cycle in living systems. Disruption of this rhythm may cause diseases. We propose an extended Drosophila circadian rhythm model incorporating cross-talk of CK2 with Per protein. We studied the model using stochastic simulation algorithm, and the behavior of the amplitude, time period and permutation entropy us identify three distinct circadian states namely, active, weak activity, active, weak activity and rhythmic death all driven by CK2. These states may correspond to distinct pathological cellular states of the living system. Noise, an important factor, has ability to switch normal circadian rhythm to any of the three aforementioned circadian states. Fluctuations in system's size, can help us in deterning the extent of noise present. We also highlighted that disruption in circadian rhythm may lead to various diseases including cancer. We present various cellular pathways driven by per mutant genes and their pathological states.