What version of InDesign? What PDF preset did you use? What PDF reader are you using to view the PDF file?
Things that can make things not appear in output
1) If you select the Image Frame or Text Frame > then go to Window>Output>Attributes
Check to see if "Non Printing" is turned on.
2) Check your Layers Panel - sometimes layers are set to Non-Printing and you can check that by looking at the Layer Name if it's set to no printing it will be in Italics.
There are other things - like Interactive objects.
Set your file to View>Overprint - do they still show up?
Or choosing an inferior PDF reader is another reason for elements not to appear.