Q: I cannot see my hard drives.

Hi Wade,

Thanks for using the Apple Support Communities. I'm sorry to hear you are having these issues with your Mac after a recent OS upgrade. I'm a bit unclear on exactly what you are seeing, but if you are not able to access your external hard drive normally, you may want to see if it is showing up in Disk Utility, and if so if Disk Utility shows any need for repairs. You may the following articles helpful:

Disk Utility (El Capitan): Repair a disk

Using Disk Utility to verify or repair disks - Apple Support

With regard to the USB Fitbit dongle, you may also find the troubleshooting steps outlined in this article useful:

OS X El Capitan: If a USB device isn’t working

Regards