Almost certainly a codec problem. This is likely the culprit:
I've already downloaded all kinds of codecs but to no avail
Yeah. That's probably your problem. "Downloading all kinds of codecs" is just asking for trouble. They often conflict with each other. I'm also not even sure what a mvw file type is. I've searched online, and all I see is this "Saber LAN Log File" (which certainly wouldn't be a media type of any kind). Either way, the file type isn't the important part of the information about the file. The more important thing is what codec the video is compressed with.
However, if you've really "downloaded all kinds of codecs" then you are likely to have "all kinds of problems", possibly including a bunch of viruses and trojans (there are lots of trojans and spyware applications that purport to be "codec packs").
Your best bet for starters is to:
1. Uninstall all of the "all kinds of codec packs" you installed.
2. Scan your system thoroughly for viruses and spyware using reliable scanners.
3. Follow these instructions:
http://www.cccp-project.net/wiki/index.php?title=Troubleshooting_Guide