I've bought an USB-to-ethernet-adapter and a minidisplay-port-to-VGA-adapter. But I can't use them at the same time. At first, I plugged those two adapters and only the USB-to-ethernet worked. I tried restarting the mac then only the VGA-adapter worked. I also tried to reinstall the OS. I'm using new 13-inch MacBook Air early 2015. OS X 10.10.3. MacBook Air, OS X Yosemite (10.10.3). Thanks for any advice.