I'm sorry but that is way too little information for informed help. We need to know more about your system and the image.
Insanity is hereditary, you get it from your children
CODEC's are the "building blocks" of AV files. They are used in the creation of AV files, the playing of AV files, the editing of AV files, and then the Exporting of AV files. This ARTICLE will give you the background.
Now, CODEC's are installed in the system, and then other programs can use many of them. Some players, like VLC and MediaPlayer Classic have a bunch of their own, so a user can become confused if they play a file in one of these. They think that they have the proper CODEC, but it's really just emulation in the player program.
The files that you are trying to Import into PrE have been created with a specific CODEC. Obviously, you either do not have that CODEC installed, or if you do, either PrE can't find it, or maybe is unable to use it to edit the AV file.
The main thing that we need to know is "what is that CODEC?" The easiest way to tell is to download, install and use the great free utility, G-Spot. It will tell you what the CODEC is, and whether you have it installed properly, plus a lot more about your AV file. That information will allow us to help you find the necessary CODEC, and hopefully, it will be one that PrE can use and edit with.
As Neale says, we need a lot more info, and that needs to start with the information that G-Spot will provide to you. Let us know what G-Sport says, and someone can instruct you as to how you should proceed.