We consider the problem of evaluating the reliability of a hierarchical computer system subject to dynamic failure behavior and common-cause failures (CCF). We present a separable solution that has low computational complexity and which is easy to integrate into existing analytical methods. The resulting approach is applicable to Markov analyses and combinatorial methods such as binary decision diagrams for the analysis of the system reliability. We present the general approach in terms of a dynamic fault tree model, and provide the analysis of an example hierarchical computer system. In particular, the example is designed to illustrate the effects of CCF on the system analysis when a cold spare or the trigger event of a functional dependency is affected by a common cause.