Cron is great for running jobs on web servers, but it's fairly common for hosting companies to either disable jobs completely or have users submit their scripts to them in order for them to be setup as a job using cron.
There is however a simple way to get round this that doesn't involve multiple support tickets to your hosting provider. It also has the added benefit of providing uptime monitoring alerts to let you know if your host is having "technical issues."
Firstly, sign up for a website monitoring service. There are many free services out there and in this example I've used Idut Uptime (http://uptime.idut.co.uk). It provides free 60 minute website monitoring (with the option to increase the monitoring frequency for a small fee). Once you have signed up go to Add a Test and select Monitor a Website.
Next put in the address of your cron script and the frequency you want to processed.
A simple but effective way to run a script periodically without the need for access to cron as shown below.