When Running iMovie Quit any applications that may be running in the background. On 64 megabyte computers, be sure Virtual Memory is turned on in the Memory control panel. Do not switch monitor resolutions while rendering is active. A tape in the camera will cause the camera to time out and go into sleep mode. If the camera requires a tape to be in the camera but does not play video through to iMovie, check that the tape's write protection tab is unlocked.
Some cameras switch to a demo mode when left on standby without a tape inserted.
Check for a demo function in your camcorder's settings menu and disable it. You can rename clips within iMovie. However, do not change the name of clips in your project folder. This will break links to the media in your project file. If you are in iMovie, choose Hide iMovie from the Application menu in the upper right corner of your screen to switch to the Finder.