Playback freezes after 2 seconds, but slider keeps moving

Equipment: Dell XPS 8910. 16 GB RAM.

Software: Current Adobe PP CC

Up until last night, my machine had zero trouble editing 4K video. But in the middle of a project, all recorded with the same camera, the playback function in the Source and Program windows no longer works. I press play, and the video only works for 2 seconds before freezing while the slider keeps moving across the screen as if the video is still playing.

I read several threads looking for help and tried many suggestions, with no solutions for my problem.

I have:

• Restarted program and PC several times
• Unchecked "Enable accelerated Intel h.264 encoding" in Media.
• Cut down on playback resolution.
• Uninstalled and reinstalled Premiere Pro CC
• Deleted my preferences folder from My Documents.
• Verified that computer has plenty of HD space and RAM. Program is only using half of PC's capability when it could use more.

Also, I should add that this problem came up in the middle of an editing session. Several other files played just fine, but now they all get bogged down in playback and freeze. I know my machine can handle the work, but it just won't now.