help on vba code to change the error date format as standard format mm/dd/yyyy

dear expert

i need urgent help on vba code to correct error date format as standard format mm/dd/mmmm.

i have set of date with time in column with improper dates in list..
like some error
1.dates 20 Apr 2013 13;45
2.19 Jul 2013 ,16;00
3.0-Jan-00 "0" or blank IF DATE IS 0 OR BLANK TAKIE CLOSE DATE
4.some column shows time only in this take close date
5.IF YEAR IS LESS OR GREATER THAN 2013 CHANGE AS 2013


find the attachment you may understand....correction coniditon.
IF TIME ONLY IN ACTIVITY START DATE TAKE CLOSE DATE
IF DATE IS 0 OR BLANK TAKIE CLOSE DATE
IF YEAR IS LESS OR GREATER THAN 2013 CHANGE AS 2013