I have a MacBookPro8,1, Intel Core i7, 2.7 GHz. I just upgraded to OS X El Capitan 10.11.1 The computer is not recognizing two USB drives that I own. External hard drives connected by the same USB port are recognized and mounted without an issue. The USB drives do not appear in Disk Utility. I've tried reseting the NVRAM. The USB drives are mounted with my MacBook Air without issue. Not sure what else to do. Any advice? Thanks.