Spell-checking (in Word, at least), is controlled at the document level, not at the application level. Accordingly, you'd need to check the spelling & grammar settings for the documents concerned.

The main ones you'll need to check are under Review>Language>Set Proofing Language. Ensure at least one proofing language appears above the bar in the upper portion of the dialog and that the 'Do not check spelling or grammar' option is not checked. For a thorough check, you should have the whole document selected when making this check. If that option is checked, none of the document will be checked. If it's shaded, some (maybe most) of the document won't be checked.

Under Review>Language>Language Preferences, make sure a proofing language has been chosen, too.

Finally, under File|Options|Proofing, there are settings that affect Word globally, including (potentially) the 'Exceptions for' at the bottom of the screen. Aside from that, if the 'all new documents' option is chosen and the 'Hide spelling errors' option is checked, that could prevent spell-checking in many documents.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]