MC has some extremley powerful tools which can probably put your filenames back to how they should be.
MC only tends to rename files when told to, so I suspect you've misunderstood one of these tools, which has caused your problems. Changing tags does not change filenames in MC, except the filename tag.
Maybe you could post some more details, where are these files based, does MC have them in the library, including the tags.
Is this on the ipod? I believe Ipods rename files to something uninteligable when stored in the IPods database, this maybe related.
It maybe an idea to calm down a bit when writing to the forum though, otherwise it tends to get peoples backs up, and they are less inclined to help. Also avoid swearing.