How can I change a font type?

Ok, so i changed my essay into wingdings font just to test how it looked like. Then I was called to answer the phone and saved my work and closed ms word 2007. When I opened it back, of course it was on wingdings. then when i changed it to Arial, it became empty square boxes. it wouldn't change back. eventhough i used different font types like tnr. Help?How can I change a font type?
At the top of most programs there is ';format'; and then click font and there are fonts to choose from.How can I change a font type?
why did u change it to windings in the first place?
In MS word select the whole document, control + A, in the font selection boxes select normal, press enter, select Times New Roman, press enter, select the size, press enter. That should do it.