You should try copying the video file to your hard disk then try playing it from there. The transfer speed from your DVD-RAM may be too slow to be able to play a video. BTW make sure DMA is enabled for that drive.
For the missing sound, use GSpot to verify that the sound codec is installed, or use a player like Media Player Classic that has codecs built-in.
The locked file is a bug with Windows Explorer, when you open a directory it scans the video files in the background and if the file is not as expected it hangs. If you reboot the PC the file will not be locked anymore, as long as you don't go back to that directory.