depends on what operating system you are running on.
Generally MySQL is stareted just before, or just after the networking subsytem starts.
If you are using windows then you may need to open the
service manager
and select the appropriate action for MySQL.
If you are usign a Linux OS then you need to do something similar, I forget waht its called (on SUSE I think it was run level manager or soemthign similar
you need to check the boot logs (Linux) or Event log (Windows) to see if MySQL is attempting to satrat but failing, and find out why