Lots of details to answer that type of question.
1. What version of Premiere Elements are you using and on what computer operating system is it running?
2. What are the properties of this GoPro Hero 2 footage that you are putting on the project's Timeline? A quick look at the video specifications for your camera suggest that you are probably recording H.264.mp4 - 1920 x 1080 at @29.97 or 30 or 25 progressive frames per second. Please confirm what is the case.
3. What are you or the program setting as the project preset to match the properties of that GoPro 2 footage? Are you working from one of the AVCHD or DSLR project presets under NTSC or PAL?
4. Is your video card/graphics card driver version up to date according to the web site of the manufacturer of that video card/graphics card?
Then the usual, just in case questions,
1. Do you have the latest version of QuickTime installed on your computer with Premiere Elements?
2. Are you running the program as Run As Administrator as well as well as from a User Account with Administrative Privileges?
Please review and then we will decide what next based on your reply.