You have not provided enough information for us to help you.
What version of Premiere Elements are you using and on what computer operating system is it running?
What are the properties of problem video and what have you or the program set as the project preset?
Is the problem confined to this one video and one project? Does the problem exist in a new project with the same video? If you
put jpeg photos or video from another source on your TImeline, does the problem exist in the current or new project?
What video card/graphics card does your computer use? One or two cards? Is the card driver up to date
according to the web site of the manufacturer of the card?
And, would you class this issue as "it worked before but not now" or "it never worked before"?
Let us start here and then decide what next.