Please give the full file name with extension and operating system you are using .
Yes.
If do not want to tell us then, check if this is not a very small file..meaning it may be incomplete download.
It may not be an executable file like TLk said.
If file says abcdef (no extension) instead of abcdef.xxx (some kind of extension) ,
...then go to file folder- view setting and uncheck "hide extension of known or system files" this will show you the extension of the file.
One thing: If you are not sure what should have been the extension of a file, then just give extension .txt, then open it with notepad.
At times possible extension is at the beginning of that garbage. Close notepad and just change the extension to what is in the beginning. (Don't do anything in notepad to change the contents) This trick works sometimes.