Q: iPod nanos won't stay connected to iTunes

while using iTunes 12 on Windows 7, our iPod nanos (both 3rd and 5th gen) will initially be recognized by iTunes, but then will automatically be disconnected before we have time to sync, make changes, etc. we have tried resetting the iPods, as well as reinstalling iTunes. We have also tried using multiple (Apple provided) USB cables and multiple USB ports directly on the PC. Nothing seems to help. We also have 7th gen nanos with lightning connectors that work with iTunes just fine - can update, sync, etc.