Failures can show up as a variety of boot problems.
Freezes, crashes, and tones are some of the failures that can occur, but they are not the only symptoms. The final condition that needs to exist is the real culprit and catalyst of the failure. To identify a potential problem with a self-powered USB device, you can attach both the AC power adapter and USB cable to the USB device and attach the other end of the AC adapter to power. Other symptoms, such as crashes and freezes shortly after or during boot up, may occur. If the system boots Mac OS and things seem to work normally, one or more of the conditions probably do not exist.