If you're talking about the extra action bars that are part of the default UI, you probably just need to go into the Blizzard interface options window and turn them back on, the same way you did to get them in the first place.
If you're talking about something else, or that doesn't work, well, there are thousands of WoW UI compilations on this site. If you want anyone to have any chance of having any idea what might be your problem, you will have to specify which one you are using.