Unable to change language

I'm currently using Excel 2007 in Spanish. I'm much more comfortable using it in English, so I have been trying to switch the language, following the normal procedure (Start menu -> All Programs -> Microsoft Office -> Microsoft Office Tools -> Microsoft Office 2007 Language Configuration) but it doesn't work. I've tried this several times, removing Spanish from the box on the right (Editing languages enabled, or something along those lines in English) so that English is the only language enabled, and setting the Primary Editing Language to English as well. I hit accept, open Excel, and it's still in Spanish. When I go back into the language configuration, English is still set as the primary editing language, but Spanish has reappeared as an enabled editing language. How can I fix this?