Can I not perform CPR?

I was at a CPR class and the instructor said that if we walked into a clients home and found them dead we do not have to perform CPR. I spoke up and said that I had an understanding that as an LPN (or PCA as most of them were) I could not make the call as to whether they were deceased or not and would have to perform CPR if they were not a DNR. What is the truth? I would hate to see one of the PCAs walk in and not perform CPR because they assumed someone was dead. They were told not to check pulses before or during CPR so that only makes it more important to perform CPR.