Help- Wierd Date Format since install

Hey all,
Since installing Office2011 my Excel and Outlook date format has defaulted to the following format:
04M12M2011 (Excel) and 12 A2011 (Outlook)
This goes for:
a) manually input data
b)data copy/pasted from other files (created prior to Office 2011, pulled off the internet, etc)
c) files opened that were created in previous versions

When attempting to reformat (in excel) to a more standard form (i.e. 12-Apr-11 or 04/12/2011) the system:
a) thinks its 4-Dec-11 or 12/04/2011
b) does not allow me to reformat at all

This is really becoming a pain.
Any ideas / suggestions?

Thanks,
-EC

 

Additional info:
I've updated system preferences date format Short, Med, Long to be all the same (i.e. 4 Jan 11), but that has not helped.
When I'm in Excel the default Date format for the cell is like this 04M12M2011 and I have to try and manually change it. Sometimes Excel allows me to change to 4-Jan-11, other times it will change to the numerical equivalent (i.e. 40880) when I try to use the quick format tool (paint brush icon), or it just does not allow me to change at all.
When cutting and pasting from a web page or a CSV import (i.e. my credit card statement) Excel formats the dates inconsistently (some are of General format 1/4/2011 and won't let me change format) and others are of Date format 04M12M2011 with the issue described above).
Still can't figure it out...

 

Figured it out!
The system preferences format was set to Custom even before I tried to set the Short, Med, Long date formats. Changing it to US did the trick!
Thanks.