http://forums.whirlpool.net.au/forum-replies-archive.cfm/818967.html said:
Hello, Kendal
I recently had a similar problem and came across your post. I had an excel sheet which had always had the right formats before, and then suddenly started showing other formats after I installed a certain program. When I checked regional settings in the control panel, it seemed right (all settings were United States). But excel kept defaulting to strangely formatted dates.
I suggest the following, as it worked for me:
Go to "regional and language options" and then "regional options" in the control panel.
Change both dropdowns (under standards and location) to an incorrect setting and apply. Then change back to the correct location and standard setting. This appears to go back to defaults for that setting, rather than retaining any customized locale formats. After I did this my dates in excel were working properly for my US format.
Good luck.
Dan