I have gone through those content and other similar posts on the forum. I still can't find the answer. Here are the spec of my computer:
Windows XP 32-bit
Core 2 Duo 3.0 Ghz
4GB DDR2 RAM
Geforce 9600 GT 1GB
Please answer the 16 questions in the first link in the Finally section.
The biggest problem is that the behavior that you describe, or similar, could have many causes. That's what Harm is trying to narrow down. With playback issues, it could be:
1.) System, especially the I/O sub-system, i.e. HDD's, and how they are allocated.
2.) Assets - what you're using as source footage
3.) Project - what Presets you are working with, and also the settings for Export
Without the answers to those questions, no one has anything to go on, and all we can do is say, "it's your system," or "it's your Assets," or "it's your Project Presets." That will not help you. With details, someone will see the possible problems, and be able to give you tips on how to eliminate the problem, or narrow down the possilbe causes.