por favor?

Ok this is so using my blog as a collective cyber help desk, but I know that some (most!) of you out there in cyber space are more techie literate than me so if anyone can help me, please let me know (post an anonymous commment, no one need ever know you were ever here, and you will be making a little sea green much happpier).

Spell check.

Why would it suddenly swap to Brazillian (Portuguese) and therefore underline all reasonably spelt English words as bad spelling? And, more importantly, how do I change it back to English?? In Word. On a Mac.