Word for Windows problems

Can anyone tell me why the speckchecker function in Word is not working in a couple of my documents, please? They are both long and they have both been reworked a lot and come through several different versions of Word (and were originally imported from LocoScript 3 via LocoScript Pro). The spell-check used to work in them, but it stopped a while back. This was probably aroiudn the time I created the current versions of these files: originally the text they contain was a series of smaller files (one chapter in each) but I merged them to make a document containing the whole book. The current format is Word for Windows XP Pro.