My Samsung BD-P1600 will play a SD disc but the rental Bluray discs won't play. Is there any way to reset the player? THX.

Maybe the rental Blu-ray disc is a copy one from a protected Blu-ray disc. You can return the disc to the owner or you can just simply remove the protection using some tools such as Leawo Blu-ray Cinavia Removal This tool is able to remove protection like cinavia and other protections such as AACS.

It is not the player you need to reset, it is the rental DVD's. They are encrypted with a code to limit the amount of time they can be watched, thereby protecting them from being stolen or not returned. Send them back to the rental company and rent the same movies again. That is your only solution. Your player will play whatever is put into it. I hope this helps.