i usually use timestamp field for the my db, so i'm not an expert
but when your are using a datetime field in mysql, when you insert the time, it has to match the exactly to the db.
for example.
datetime(6) // field type in mysqldb
you have to put you data in this style:
YYMMDD
so when you a value you have to do something like this: (in php)
date("ymd")
if the way you try to insert the date and it doesn't match exactly to the format of the datetime field in mysql you will get a bunch of zeros.
references:
http://www.mysql.com/doc/en/DATETIME.html
http://www.php.net/manual/en/function.date.php
i hope i make myself clear.