Question: I'm using Word 2010, and I'm working on a guide where contents to be added inside a table of three cells.
I have an issue with couple of pages where I couldn't insert the cursor into the left cell to add a text. It works in some of the pages, but not for the others.

I checked the Developer tab to see if any protection is active but nothing. I tried also to copy those tables into a new word, but got same result.

I couldn't find an answer online. So I appreciate your assistance.

Answer: 
The problem with my file was that Word had arbitrarily set the point size to 0.5 in all the empty cells. Once I reset the point size to 10, I could enter text.
My table span was over 4 pages with only 1 page being affected. I put the cursor in the column I was having trouble inserting text and right clicked and under Table Properties check the column size. I did this on several pages and realized that the one I could not edit had sizes for the columns on that page, but the other ones were dithered at a whole size of 10.1. Also I preview my pages at 50 % to only focus on the columns and this help me realize when I had clicked the column that had the problem it highlighted the following page. I turned on the paragraph marker and notice I had a hard return at the top of the page with the problem column, so I deleted it and at the bottom of that page I place a page break to move the border row back to the top of the next page. This was definitely one I had seen before.