The computer does not see the fenix 5x (usb mode,sofware 5.10)

Not sure how much help this will be, but I had the same issue on a Mac, and solved it with a restart, which also prompted an update to Express.

Restart Fenix, restart computer, try another USB port. One or all of these tricks together should solve the problem.

I've already tried it (Restart Fenix, restart computer, try another USB port).
Probably there will be a warranty repair :(

Try another computer with usb 2.0, try to use usb hub in between.

It's most likely the cable, nothing you can do either the watch or the cable must be replaced.

I had a similar issue on my Windows 10 laptop, but it worked on two other laptops running 64 bit Windows 10. I thought it might be a driver issue but I never did end up getting it working and didn't pursue any further with Garmin because I had other options. Try at least one other machine before chalking it up to a cable issue.

I have it time to time and solution is very simple. Connect the watch to the USB port and then restart it. I don't know why but then it works. This advice comes from one of the topics and since I started to use worked always.

Update:

1. Remove the watch from Express.
2. Connect to USB
3. Restart
4. Should work.

Is this something simple like the windows power saving the USB - two simple checks in device manager and power options might help

http://helpdeskgeek.com/windows-xp-tips/prevent-windows-from-powering-off-usb-device/
http://www.techsupportalert.com/content/how-fix-annoying-windows-usb-problem.htm