spell check is not working...how do I turn it on? (MS Word 2013)

Yes, I second this. I did a mail merge into Word from an Excel document. There were several misspellings but Word was not showing any spelling errors. I could be wrong, but it appears that when merging from Excel, it automatically defaults to "do not check for spelling or grammar" under the language settings. No matter how many times I uncheck it, it still re-checks itself. 

My solution: Select all the text and hit Ctrl + spacebar. Once you do this, two things happen: 1) the "do not check for spelling and grammar" automatically becomes unchecked, and 2) any misspellings and grammar issues will be revealed. (Unfortunately it also removes formatting such as bold, italics, etc.) 

Mail merge does not set all of the text to "do not check" The text that was merged in does keep this setting from the field. There is no way to change that. These will contain data from the data file.

If all of the merge fields are formatted the same, you could create a mymergefield character style set to not check spelling or grammar. Then have a second one checkmergefield character style based on the first and set to check spelling and grammar. Upon completing the merge to a new document, you could use the replace feature to change from the no-checking style to the checking style.

You could record a macro doing the replace and run this macro when you complete merges.

To me, it is simpler to just proof your data file.

In one merge that I do regularly, I have one merge field formatted to be bold and pink because that field often does contain information that I do not want included in the document going out. I have a finishing macro that removes the formatting with the replace function.

Mail Merge

After some thought, see next for a replace without using Styles.

Yes, I second this. I did a mail merge into Word from an Excel document. There were several misspellings but Word was not showing any spelling errors. I could be wrong, but it appears that when merging from Excel, it automatically defaults to "do not check for spelling or grammar" under the language settings. No matter how many times I uncheck it, it still re-checks itself. 

My solution: Select all the text and hit Ctrl + spacebar. Once you do this, two things happen: 1) the "do not check for spelling and grammar" automatically becomes unchecked, and 2) any misspellings and grammar issues will be revealed. (Unfortunately it also removes formatting such as bold, italics, etc.)

I had this same problem and could not figure out why, I opened a new document pasted my text in and still the same problem.

I finally figured out whats going on, my text was formatted to not search for spelling errors. I was working off a document that was originally used as Mail Merge Template for Salesforce our CRM Software. Obviously it is wise to not want your mail-merge text spell checked, it is full of nonsensical "words" that only make sense one the merge is complete. 

So I copied the text and pasted it into a new document as plain text, and presto spell check worked great. 

Boom!

After unchecking the box, you need to click on the "Set As Default" button at the bottom of the Language dialog.  When you do that, a dialog will appear that among other things will advise that "This change will affect all new documents based on the NORMAL template"  If after doing that, the setting is not being retained, it may indicate that there is an issue with the saving of the Normal.dotm template.