It's not enough to import the files into a Premiere Elements project. You have to physically copy the files from the camcorder to your hard drive. The easiest way to do this is to attach the camcorder to your computer and use the Video Importer under Premiere Elements' Get Media/From Flip AVCHD and Hard Disk Camera.
If you don't physically copy or download the video from the camcorder, the connection to the files will be lost as soon as you disconnect the camcorder.
The other possibility is that you didn't let the program fully conform your video after you added it before you started editing it. You must wait for your imported video to be fully conformed. (You can watch the progress on the lower right of the program's interface.)
Also, you don't say but I assume that, when you started your project, you set it up for Full AVCHD video 1920x1080 (assuming you shot in FXP or MXP mode) and that you also selected the correct audio settings (depending on whether you shot your video in stereo or 5.1 audio). If you haven't got your project set up correctly, your video will not behave correctly.
As well as what Steve said (this may be done by the Video Importer process he described) I have read that you do not just copy the individual files to a folder on your hard drive, you need to copy the entire folder, with files, from camera to hard drive
I was in the organizer and went to "file. get photos and video from.camera and card reader......" some of the files came over and some only parts came over.