So one PC has MC14 and all video files except DVD cause crashes. Another PC has MC15 and the behavior is similar. By DVD, do you mean DVD from the original disc or DVD that is ripped to hard drive? If the latter, is the format "VIDEO_TS folder and several files in it"? I'd like to see the DirectShow graph from DVD playback. Please follow glynor's instructions here:
http://yabb.jriver.com/interact/index.php?topic=59603.msg402889#msg402889 and post the graph.
When you try to play AVI (for example), what exactly happens? Does it play at all or does it crash immediately?
Have you installed any DirectShow filters and you have configured MC's video playback anyhow or is everything set to defult? If you can play an AVI file before it crashes, could you post the graph info from such playback attempt.
Regarding your PCs, what operating systems are you using and have you updated them? If you have an older OS, is DirectX up-to-date? (I think Windows 7 updates it it automatically). What graphics cards (or integrated graphics) do you have and are the graphics drivers up-to-date?
EDIT
...They all crash MC 14 and 15, on all three computers of mine ...
I just noticed that you mentioned also a third computer. Do all three computers always crash in a similar way?