You can try opening the original .srt file in Microsoft Word and see if it can detect the encoding - or if you use Firefox, just drag it onto the window, click 'View' > 'Character Encoding' and select one of the types to see if it can make a match.
If Word can correct it, save it as unicode - If Firefox shows it ok, copy and paste into NotePad and save.
Other than that, I can't offer anything except try for a different source.
This is an example of a Greek sub that was detected in Firefox.
Why not download New English Subtitles instead of messing around with these. Your current Subtitles most likely are in some ODD language that your software does not recognize.
