File conversion makes document unreadable

I opened a word document written last year. (I have Word 2003). It asked
whether I would like to have it converted. I ticked yes to the default box.
It has converted to something which comes as boxes on a previously normal
word text. When I try to open the document, it says select the encoding that
makes the document readable. There are 3 options, including MS-Dos, default
Windows and Other. None of the options works to make the document readable.
Help. Its an important document
.