The most common reason why only one flash drive is usble when multiple USBs are connected is due to a device signature collision.
If you are dealing with bootable devices and seeing this problem, we are confident a collision is the issue. If you are not dealing with a bootable device, then our information below will, probably, not help.
What is a USB signature collision?
A signature collision can happen on any bootable device, so Compact Flash cards, SD cards, microSD cards and USB flash drives. A disk signature is a unique identifier number (UID). It is a unique identifier stored as part of the MBR (Master Boot Record) for an operating system loaded on the device. The operating system will use the UID to identify and distinguish between storage devices. It is commonly made up of eight alphanumeric characters. A disk collision occurs when your operating system (Windows) detects that there are two disks with identical signatures.
For Windows 7, 8, 8.1 and 10, these versions of Windows will disable the second drive and will not allow that second volume to mount until the disk collision has been rectified. If you are reading this article, chances are, this is exactly what is happening to you.
The first thing to do is navigate to the Disk Management tool with in Windows. To do this, use the search tool and type in Disk Management. This will take you to the utility that Windows offers. Here you can see your multiple devices connected. If you click or hover over the device not working you will see one of two messages:Continue Reading