Problem playing mp4 files and to transport txt and srt files

Hello people.
I have problem with the fonts. Unfortunatelly I don't know what brought the problem so what informations would help you to understand it. I'll give some, but I don't know if they are involved or not.
I clean installed W7 x64 prem. before some months. Not any codecs. Now I cannot play mp4 with any media player eg.vlc, real or Windows player.
After the clean installation(W7), I transported all my data from an external drive back. The most .txt files became "Chinese (I mean not readable). I tried to convert them to unicode with not succes. I must tell you that I know nothing about Ansi unicode utf-8 ...so everything I was doing was by blind-luck...
Last days I was trying to download .srt subtitles for some movies. It happened the same story..."Chiness"...Can anyone help me or give me a direction about what I have to do? , where is the problem for the mp4? (normaly I think W.m.player is able to play).
Also if is possible to read (convert), the files that are already destroed.
Thanks a lot.

Thanks for responding.
My Os is in English, but I'm Greek so The .txt, .srt files are in Greek.
I attach a file that you can see what I mean "unreadable like Chiness". Is a .srt file but the same unreadable fonts are when I'm transporting .txt files from the external disk back to my C:
This .srt I downloaded .zip or .rar, but when I'm extracting the files they become like you see.
If I remember well before the "clean install" i did, when I unziped .srt files everything was ok.
(when you said maybe I'm missing fonts what did you mean, and what I should do?)
Thanks a lot. ( I can give any other information if need it.)

Thanks MilesAhead, I'll try it. Have a nice night.