I am working on a page someone else created as a master page, and want to add a text box to the page. I created the box and placed my text in it, but the text is not visible. If I drag the text box off the page and then drag it back on, the text is visible for less than a second then disappears again. Any thoughts?
I agree with what Scott commented about.
This could very well be a text wrap issue. In order to make that specific text box be independent of the text wrap settings, select the text frame and then navigate to Object > Text Frame Options, then select the "Ignore Text Wrap" option.
Try creating a new master page and put your text box on that. If it shows up, there's something on the existing master page which is blocking your text box.
I've also seen this happen when someone has inadvertently set "non printing" as their default by turning it on with no selection. If you are viewing in print preview mode, the item will immediately disappear.