You may want to "cat /etc/rc.log | grep cron"
This will tell you if cron tried to start at boot with an rc script and if it had a problem starting.
If not, you need to setup a link to: "/sbin/init.d/cron" in "/sbin/rc.2/" or "/sbin/rc.3/" depending on your active run level at boot. Probably: "/sbin/rc3.d".
When creating the link, note the "S" and "K" numbers "S"=start, "K"=kill both with the same unique number, this number determines when it will run in the succession.