Microsoft PowerPoint doesn't check the spelling in embedded objects such as charts, in special text effects such as WordArt, or in inserted objects such as Microsoft Word documents.
Do one of the following:
Check spelling in the whole presentation
Note If the insertion point is in the notes pane or slide pane, the spelling check alternates checking between the two. If the insertion point is on the Outline tab, all the slides are checked first, then all the notes.
Check spelling as you type
Note In the Options dialog box, use the other check boxes under Spelling to further control the spelling checks.