Don't quite understand your issue - you seem to contradict what you are saying, but if you are getting a dark Grey then maybe you need to change your preferences "Thumbnails to show in video events". Set to "All".
I guess what I was trying to say is that timelines for the video and audio are now a dark gray. Clips that I highlight in the trimmer window will preview ok, but when I try to preview the timeline video, nothing shows in the preview window.
I tried to hit the mute button to see if the video would show up. It didn't. Is there a way to show you a screen shot of what I'm seeing? I'm new to this forum.
If you have an external location to host a still (like a flickr account) you could then link to it here. There's a sticky post that explains the available tags. It's at the top of the main thread list.
Doing what you did have solved the problem but you still don't know what the problem was :-(
If it happens again, you still won't be able to properly solve it which is why it's always better to find out what happened to cause it initially.
Like a lot of users here, I have too many custom presets to make using Ctrl+Shift a useful option as these get wiped out immediately.