Can you please give us the full details of that source footage, and also the details of your I/O sub-system, i.e. your HDD's, their size, speed, controller type, free space, and how you have them allocated. Knowing the Project Preset that you chose will be helpful. It should match your source footage perfectly.
This ARTICLE will tell you what will be so very important, and even tell you how to gather some of that detail.
Also, in your Timeline, do you have a red line above these Clips?
PS - Welcome to the forum!
- Install all Windows updates
- Install latest version of QuickTime (v7.6.6 at time of writing)
- Install most recent graphics and sound drivers from the manufacturers web sites
- Run Disk Cleanup
- Run Defragmenter
- Post back here with the necessary information described here: Got a Problem? How to Get Started
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