Solved Video and Audio problems

I'm using Movie Studio Platinum 13. I'm making a compilation video. Everything was going great till one day, one of the videos that I put on the timeline wouldn't play. In the preview window there is no video but there is audio. This is now happening for other random video clips I have on the timeline already as well as videos in the explorer tab. MSP will sometimes freeze as well and stop responding and then crash. If I start another project, these same video clips work fine. What could have I done or does this sound like a software issue? If I uninstall and reinstall will my compilation project be lost? Also, some of the videos that do not play, in the explorer window where the thumbnails are, the video info will say, "Stream attributes could not be determined", while some of the video files that do not play, will still show the videos resolution, frame rate and video length.

Normally if you cannot see the Video but can hear the Audio, that means the video is using a Video Codec that is not supported by Movie Studio.
There are a huge variety of Video Codecs and Formats in use today and not all can be supported by just one program.

What is the file extension of the problem videos ?
Where did they come from ? A camera or the Internet ?
What type of camera ?

My guess is that do have some videos that are not supported. This can cause problems with thumbnail creation in the Explorer tab, which makes the problem worse.

I would suggest the first thing you do is a full program reset - this will restore all settings and is better than re-installing the program.
This will clean the Movie Studio cache and delete any dodgy thumbnails that may be causing the problem.
Do this:
Turn Movie Studio Off.
Hold down CONTROL and SHIFT keys at the same time AND ALSO AT THE SAME TIME double click program icon on Desktop to Boot program.
Window will pop up.
Select Delete Cache and Yes.
This will restore program to Factory Default Settings.

If you want to use videos that are not supported, you will have to convert them into a Movie Studio friendly codec/format before you attempt to import them.
I have a tutorial that explains this here:
How to Convert Video into Different Video Codecs and Formats

Regards
Derek.

Thanks for the reply Derek.

All the video files are either .MP4 or .MOV, and come from either a Panasonic HDC-TM90 video camera, an IPhone or a Samsung Galaxy phone.

Every time I open this project, it seems to be different video clips that are doing this. But if I start a new project, every thing works fine. And the same video files play correctly. That makes me feel like its something with this particular project.

I know there is a limit to the number of tracks I can have in a project, but is there a limit to the number of video clips I can have on the timeline?

Maybe my processor can't keep up with this particular project, because most of the time when editing this project the program will stop responding and crash. My CPU is Intel i7-4700 MQ 2.40 GHZ, with 8 GB RAM, and running Windows 8.1.

If I do the full program reset, that you suggested, will that delete this project? If it will, I would like to try that as a last resort, because I've put some time and effort into this project thus far.

I didn't mean to underline and bold that much of my last reply. I apologize for that.

A full program reset will not delete any of your saved projects, it only deletes temporary cache files.

I suggest you start your project again - that is what I would do.
Just take it slowly and make sure everything is working. If it stops working, take note of what you just added or did and then reverse it.

Make sure you have Apple Quicktime for Windows installed - you must have this installed for .mov videos to work properly.
Also make sure you do not have K-Lite Codec Pack installed - this will destroy the Windows Registry entries for Movie Studio and Vegas Pro.