connected to a powered USB hub on my desktop because it will not reach my PC. Can I safely replace the USB cable that came with the unit with a standard 6-foot USB cable?
Yes, USB is USB. Also, why will my pc not boot when I have the external drive that is plugged
into the hub and powered on?
Some older motherboards are like that. If you have a USB drive plugged in and active they hang at post. Trying configuring your BIOS boot sequence to include that drive.
