Please use meaningful subject lines.

Sort the rows on the first five columns

In the column after the last column used in row 2 if that is the first row of
the matrix  put the following (I am assuming CW2) :

=IF((A2=A1)*(B2=B1)*(C2=C1)*(D2=D1)*(E2=E1),CW1+1,1)

Now copy that down the 300 rows

The count will increment until one of the first five cells changes.