Date in Excel, Wrong cell format

So I attached two pictures.

the first picture shows the cells with format = "Date"
the second picture shows the cells with format = "Text"

as u can see, many of the cells are not changing, which is wrong ..
I don't understand whats the problem is and I would be grateful if someone can guide me on how to make all these cells in the correct format.

My main problem is sorting, I want to be able to sort by date and since some of these cells contain "Text" and not "Date" format its sorting is turning out to be wrong ...
(I'm getting 2005, 2006, 2007, 2009, 2010, 2011, 2005, 2006, 2007...)
As in the "Date" formatted cells first followed by the "Text" formatted cells at the end of the document.

Any help is appreciated. Thank you