It is possible that one of your card is defective.
1. Try playing games with one card at a time to see if either one will cause this problem. If it does then you will know for sure.
2. Try uninstalling the NVIDIA driver completely and reinstalling to the latest driver on NVIDIA.com
3. To get your replacement. Fill out this form. http://www.palit.biz/us/rma/rma.php
and if you have problem filling out form please email us at GRACOM_RMA@live.com