H264 is an mpeg4 codec. Although .h264 can be used as the extension, it is not that common. If you don't have a utility such as MediaInfo or GSpot to determine what it is, try changing the extension to .mp4 . It could also be a .avi or .mkv.
The .h264 file is a video stream so you might have to put it inside a container (Matroska would be my recommendation), if VLC or MPC-HC can't open it. MKVtoolnix can place it in a Matroska container, but keep in mind that H.264 streams need you to specify the FPS when putting it in the container. Otherwise it'll be multiplexed at 25 FPS, which may be wrong.