1. Verify settings in Word 2007:
a. Open a document that has this problem, press Ctrl+A to select all of
the text.
b. Click on Review tab | Proofing: Set Language | <choose your language>
| uncheck the "Detect language automatically" and "Do not check spelling
or grammar" boxes | Default | OK.
c. Click on Office Button | Word Options | Proofing | check the "Check
spelling as you type" and "Check grammar with spelling" boxes | uncheck
the "Hide spelling errors in this document only" and "Hide grammar
errors in this document only" boxes | OK.
2. If the previous suggestion doesn't help, then in Word 2007 click on
Office Button | Word Options | Add-Ins | Manage: Disabled Items. If you
see any disabled items that relate to spelling, try enabling them.
3. If the previous two suggestions don't help, then:
a. Close Word and any other open applications.
b. Click on Start | Run | Open: regedit .
c. If the key "HKEY_CURRENT_USER\Software\Microsoft\Shared
Tools\Proofing Tools\1.0\Override" exists, delete it.
d. Exit regedit.
e. Restart your computer.