We definitely need more information about your PC, Camcorder,Video clips and how those clips got onto the PC. See Got a problem? Here's how best to ask for help
Insanity is hereditary, you get it from your children
Let me jump to a conclusion
Press Enter to render the timeline after editing. Then try playback and let us know. Project presets are vital here, but rendering does not hurt..
And, as we continually remind people on this forum, much depends on what kind of camcorder your video came from and how you got it into your computer.
It's very important that your source video match your project settings exactly.
And it's just as important to note that some formats (i.e., video from still camera, video from a Flip cam) will not work in Premiere Elements without being converted first.
Also, as VDOSurfer indicates, if you've got red lines above your clips on your timeline, you need to render your timeline. Certain video formats (such as AVCHD) need to be constantly rendered even to run smoothly on a quad core processor. (What are your computer's specs?)
While you are gathering the info, that Neale's linked article asks for, here are some other articles, that will help, first getting your computer ready for an editing session, and then giving you some background on file types, what they mean and then a little info on CODEC's, the building blocks of Audio-Video files:
Tuning your system is covered in both this ARTICLE, and in several FAQ entries, found at the right-hand side of the main forum page.
This ARTICLE discusses file types and explains how they are just "wrappers," which can contain many things.
This ARTICLE goes into a bit more detail on CODEC's, the building-blocks of AV files.
I also recommend Steve Grisetti's books on PrE, his Learning Series and his Boot Camp series, all available on Muvipix.