@nick – upgraded from 4.2.X to 4.3? or 4.3 to 4.3.03?
Trying to figure out what is going on.
All 4.3 installs should have data extensions active by default. The only way I can think of to make that not happen is by either having Super Extendo (an old and should-never-be-used 4.X plugin) installed OR via corrupt SLP options entries that we may be able to fix with Janitor.
Can you include a screen shot of the Plugin / Environment page and show the PHP and other versions? That may help me decipher what is going wrong with your update.