Assuming you have proper ventilation, it is entirely possible the 6870 is defective. Is the 6870 O.C.'d? You can check the cards sensor readings using CCC. What do you mean by warm? Does the card work at first boot? If it does and then dies after some use, it is probably defective. When it heats up the bad component fails or it might be a connection (solder) that expands when hot and opens. Just as a check, you might set all you bios values to default and see if the card works. Don't know your O.C. settings but you may have affected the values to the slots?