A single photon avalanche diode (SPAD) receiver can provide a significantly improved detection sensitivity over conventional photodiodes. However, upon detecting a photon, the SPAD receiver is unable to respond to subsequent incident photons for a certain period of time called dead time. When the SPAD receiver is counting in consecutive intervals and its dead time is relatively long compared to the counting interval, the dead time in one interval may overlap the next intervals, causing counting losses in those intervals. In this paper, the photocount statistics of an active quenching SPAD receiver with a long dead time is investigated. While detecting in consecutive time intervals, the SPAD receiver can be modeled as a Markov chain. It is shown that the SPAD experiences a transient period, before eventually reaching its steady state. The duration of the transient period increases with both the dead time and the signal photon rate. The bit error performance of the system with an on-off keying (OOK) modulated signal is also evaluated. Our results show that the SPAD's dead time significantly degrades the error performance of high data rate links.