This is happening because you are not assigned any tab groups that have access to Design Reports.
In Method go to Customize > Tab groups it will list all the tab groups that currently exist you should see a checkbox for design reports. Make sure that atleast one of the tab groups you are assigned to has this checked.
To assign Tab Group go to Customize > Users, edit a user and go to step 4.
Note that if you are not the admin on the account you may not have access to the customize tab.