Try installing Webmin, then use webmin to configure the crontab table. Compare webmin's output with your hand-created table to see what's different. This might help you to determine the problem. Also, it is possible to restrict cron to only run for specific users. If this is the case on your system you have 2 options. 1. Enable cron for your username 2. put your crontab entries in the root crontab. Either way your crontab entries should work.
Allowing a program like webmin (
www.webmin.com) to create a system configuration for you and then tweaking the created table is a great way to learn. Webmin is a very small web server that runs on your system through your web browser (
http://localhost:10000) If you are running a system that restricts root access (like Ubuntu) you will need to use a non-privileged user with root access via sudo to login to webmin, otherwise login with root and the root password to add your user name to the user table. Webmin's creator is very helpful to new users answering help requests quickly and correctly.