Last week, one of my regular home computer repair clients called about their Dell Windows computer. It wouldn’t complete the Windows startup cycle. As the computer booted, it displayed the Windows splash screen, then stalled at a black screen. A few days ago Windows 7 updated to Windows 10 and It worked for a few days until now. Upon arriving I ran the built-in Dell hardware BIOS diagnostics and they passed so it probably isn’t a hardware problem. I Rebooted the computer and still a black screen. I asked some more questions of the owner and discovered about the same time, they were installing and configuring a fitbit USB device to sync with a Fitbit wristband activity tracker. I shut down the computer with the power switch and found the Fitbit USB device in the front panel port which I unplugged. The computer was started again and it booted Windows 10 and runs normally. I shutdown and restarted the computer one more time to be sure and Windows 10 was fine. My hypothesis is the computer was trying to boot from the USB Fitbit device before the hard drive and failed.