Hmmm, now i´m a little bit in panik, to ask my question:-(
I´ve gotten my 5th RX470 today. I have 2 X 750CM+80 Corsair. OS can´t install the driver for the 5. card. doesn´t matter wich one it is.
Is there might be a limitation in Window 7 proff.? All Cards are working fine, as long as they are not the  last one, installed.