I had been back and forth with this problem since asking about it, and finally found something that seems to have fixed it with 280.26.
- Open the NVIDIA Control Panel
- Select 3D Settings / Manage 3D Settings
- On the Global Settings tab, select "Power Management Mode" setting
- Change Power Management Mode to "Prefer Maximum Performance"
- Select the "Apply" button
- Select the Program Settings tab
- Select the "Add" button and browse to C:\Program Files\CyberLink\PowerDirector\
- Select PDR9.exe and click on Open
- Under "Select a program to customize:" ensure PDR9.exe is selected
- Change Power Management Mode to "Prefer Maximum Performance"
- Select the "Apply" button.
- Close the NVIDIA Control Panel and reboot.
Adding the program and changing the the setting specifically for PDR9.exe probably is not necessary after changing the Global setting, but I did it just to make sure there were no excuses.
After making the above changes I've been able to split, move, expand and contract clips and do everything that caused the "driver not responding" error before, with no problems.
Hopefully this will work for someone else, too.