by Howard Miller.
What does disapeared look like? Do you get a message or anything?
Is there any possibility at all that something (however trivial) went wrong with the upgrade between 1.9.x and 2.x and you had to restart the upgrade? If this happens you MUST restore everything from backup (especially the files area), fix the problem and start again. The file structure has completely changed in Moodle 2 and a failed upgrade can leave the files in a corrupted state.