Microsoft Word 2004 Outlining

[rubes6]

I am running the Mac version of Microsoft Office 2004 including MS Word. In writing in outline format, for some reason I can't figure out how to indent to a new outline level by just using the tab key (I used to be able to do this). By this I mean I run an outline in the format 1, a, i, etc. and when I enter return, a subsequent number or letter in the same level will come next in the autoformat, but if I press tab, it just indents the same line instead of creating a new level (going from 1 to a by pressing tab). Any suggestions on how to go back to the good ole' days of being able to do this? Thanks for helping me out!!!