how to delete unwanted rows?

in the excel file i wanted to delete the blank rows which come in between data rows. i applied the following with negative result. select entire column. auto filter. filter for blanks. got all the blank rows selected . then i pressed delete key. nothing happened.

i tried the other way and got the result. select the entire col. press f5= special blanks. go to the ribbon. delete- drop down arrow and select entire sheet rows. done

anybody tell me why the first option didn't work.

in my worksheet there are unwanted entries "3 years ago" (row numbers-2,5,10,14,19,25,31,37,43,49,55,61,67)how to delete those entries?

my worksheet contains duplicate entries(Row numbers-3,8,12,16,22,28,34,40,46,52,58,64,70). kindly tell me how to avoid the duplicate entries.