|Since I can't see your spreadsheet from where I'm sitting, it's kind of hard to diagnose your problem.|
DATEVALUE will return a #VALUE error if it can't convert the text into a date.
For example, applying DATEVALUE to this should work:
March 1, 2010
But this would return #VALUE because Excel wouldn't recognize it as a date since it's missing the comma:
March 1 2010
In general the text has to appear in the cell looking like one of Excel's date formats in order for DATEVALUE to work.
If you type in a date and it doesn't convert, check the formatting and tell us what it says.