I'm not familiar with the K4D and how it connects to the PC (I assume via a single USB cable?), or if it needs a manufacturer supplied driver, but the first thing I would try is installing FLRIG for rig control and see if that works: http://www.w1hkj.com/files/flrig/
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And then troubleshoot the problem after the contest. Not necessarily in this order:
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1. Try a different USB cable.
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2. If that doesn't work, Roll Back Driver in Device Manager.
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3. If that doesn't work, Uninstall Device in Device Manager, unplug device, reboot, plug device back in.
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4. If that doesn't work, do a Windows Refresh (or what ever it's called)
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5a. If using the Hamlib built-in to FLDIGI, try the latest alpha release of FLDIGI from: http://www.w1hkj.com/alpha/
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5b. If using the stand-alone version of Hamlib, try reinstalling it.
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6. If THAT doesn't work, do a clean install of Windows.
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Good luck!
Steve K4RVA
Steve K4RVA