Are you trying to save your photograph as a JEPG and not finding this option in Save dialog OR facing the same problem for other file-format, here is a short answer for your problem.
Most of the times, we have observed this sort of problems with folks using DSLRs. This happens when you try to save 16-bit photographs into other file-format. So simple solution is to change the image mode to 8-bit and try saving again. Here are two simple ways of changing image mode of a Photograph -
1. In Adobe Camera Raw Dialog, there is a small dropdown in the bottom through which you can change it to 8-bit and Open image in Editor workspace to save it further.
2. Other way is through Image Menu. There is an option Mode which helps in changing image mode.
Feel free to post your further queries on this topic or Adobe Photoshop Elements, through comments.