Hi all, I sold my working Sapphire AMD Radeon HD 7950 Mac Edition 3GB Video Card and the buyer says "boot screen on the monitor is black and blank. The boot sound chimes repeatedly and does not stop". We both have 2009 Mac Pro flashed to 2010. 5,1 on OSX MOJAVE and the card is just plug and play on my Mac. When he switches back to his RX580 the Mac boots up normally. He is using the correct power cables. Any suggestions? Thank you in advance for your help.