Try what Rasmith said above to test if it's a USB issue. If it's not a USB issue, perform the below.
Connect your device to your computer. Open up Run and type in 'devmgmt.msc' without the quotes. You should get a window with all your devices connected/present. Look for anything that includes Apple in the name with a little yellow triangle with an exclamation point on it. Right click it, and click uninstall driver. If you don't see it immediately, check under Universal Serial Bus Controller (or USB, not sure which one Windows 8.1 utilizes), and again look for the little triangle next to it. Right click and uninstall the driver.
Unplug your device, and perform a cold boot of your computer (hold down the power button until the computer shuts off, do not go to Start > Power Off). Boot your computer up again, and plug in your device. You should get the tone of new hardware being connected and that Windows is looking for a driver. See if that resolves the issue.
If this does not resolve the issue, uninstall iTunes, cold boot, and reinstall iTunes.