I spent a couple hours uninstalling and reinstalling to try to fix this problem. Maybe repeating this section from (http://granite.ab.ca/access/developeredition2007faq.htm) will stop you from doing the same.
Q: I installed the developer extensions but can't find the Developer option in the Office button.
From a fellow Access MVP - The Add-in will disable itself if you switch between Access versions. So if he has more than the 2007 edition installed and he opened the earlier edition after the installation he will need to manually re-enable it through the Access Options dialog (Office Button--Access Options--Add-ins--Manage: COM Add-ins--Go...--Check Microsoft Office Access Developer Extensions COM Add-in--Ok--Close Access Options and look under the Office button again).