I also have similar problem with 2x 280x. One card is hashing but the other one is not disabled but hashing only 10kh/s. Do I need to upgrade memory to 16GB?
You can launch one miner per card to make sure they work fine and there is enough memory.
Should I have to check the memory status in task manager? And if there is not enough free memory should i buy more? I do not have problem with upgrading just asking if this will help. Thank you
EDIT: I have 8GB right now.
Start one miner copy with -d 0 and another with -d 1 to see if they work fine.
One miner with -d 0 and -I 16 in still not hashing but consumes more than 2GB free memory, and if I run only the seccond miner -d 1 and - 16 it is hashing fine and consuming almost nothing from free memory.