I know that if you try to connect to tether on a computer after it was asleep it doesn't work. I was just wondering if they have fixed that problem yet; I don't like to turn my computer on and off so often...
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This issue has always been dependent on the PC hardware Tether is being ran on.
Could you try logging out of Windows and logging back in without rebooting and try Tether afterward?
The developers are always trying to improve the compatibility of Tether but the sleep issue is a tough one to nail down since not everyone experiences this.