Once a portlet is hidden on a portal page it can be a little confusing how to get it back on the page. Luckily it is pretty simple once you know how to do it. A hidden portlet is moved to a whole seperate section of the page, which isn't displayed by default.
In order to re-enable hidden portlets follow these steps:
1) Go into edit mode.
2) In the left hand panel (the site manager) click on the three cog icon to enable advanced mode.
3) There will now be a new icon added to the row of icons. This icon is a rectangle that when you hover over it says "Show hidden content container on pages"
When you click on this new icon, on the top of the page on the right will be a section that has all the hidden portlets.
You then drag them down or use the move down to put them back in the unhidden section.
4) Now the portlet will be unhidden. Go ahead and take the page out of edit mode and you will see it again