Well, all in all the first thing you should do is remove
ANY and
ALL mods you know for a
FACT affect action-bars, a few examples of such are Domino's, Macaroon, Bongo's, etc. If everything else works fine obviously you installed either conflicting action bar mods or installed one and never set it up so it is appearing blank.
Best to start from scratch in a situation like this, if you
CANNOT identify which mod is causing your action bars to disappear my suggestion then is to run the
Blizzard Repair Utility and have it reset your cache, interface, and configuration.
Please note that this will remove ALL custom files and settings, and will basically run the game clean like a fresh install.
You will need to re-download and install any mods you want, and then set them up accordingly; and try not to install and overabundance of add-ons or you'll find yourself in the same situation you are in now.
As a general rule, you usually don't want to have more than one add-on installed for one purpose, e.g., if you have a mod installed that effects your minimap, like
iMinimap, you
SHOULD NOT also install another mod that does the
SAME THING, like
dMinimap.