Keyword Analysis & Research: why won't excel let me change the date format

Keyword Analysis

Keyword	CPC	PCC	Volume	Score	Length of keyword
why won't excel let me change the date format	1.88	0.8	3962	77	45
why	1.77	0.1	7430	45	3
won't	1.41	0.4	5711	85	5
excel	0.83	0.8	3013	39	5
let	0.54	0.8	5785	33	3
me	0.44	0.9	6544	52	2
change	1.68	0.5	5670	60	6
the	0.75	0.6	121	9	3
date	0.53	0.5	50	76	4
format	0.3	0.5	8809	19	6

Keyword	CPC	PCC	Volume	Score
why won't excel let me change the date format	0.6	0.7	7790	87