I have a pretty simple question:

I have an Asterisk system running on Centos (6 I believe), and I had set up a crontask so that the computer would reboot every morning (I had some issues with connectivity). Now that is fixed and I want to see if I can keep the Asterisk box running continuously. I have commented out ("#") the crontab line and saved it (as Admin), but my computer keeps rebooting at 4 ...

Do I need to do anything else other than commenting out the line?

I would say you commented out another line, not the relevant one. Or it is configured in a different way. But without knowing the system hard to say more.

in addition, where did you create the task? If it is a system cron job i.e /etc/crontab then the system should automatically pick up the changes. If it is a root cron job and you edited /var/spool/cron/root directly then you need to restart crond.

Thanks. That was quick. Kudos.

To be honest I am not sure how I set that up. It's been a while ...

But commenting out the line in /etc/crontab does not do anything (there is only one line in there, so no chance I commented out the wrong line).

But I see the same line in the /var/spool/cron/root file (not commented out). I renamed the file to root_old, but I am not sure if that would do it or not. Is this file created automatically from some other configuration file, so that it comes back when the computer is rebooted, or will my renaming work?

can you please show us the output of:

You can look at the cron log file to see where/what i.e. user or system is running your task.
/var/log/cron

If you manually edited/renamed the /var/spool/cron/root file instead of using crontab -e (as root) the system would not pickup the changes until you restart crond.

/var/spool/cron/root is viewed with crontab -l and edited with crontab -e (using EDITOR...usually vim, tho that's configurable)
...michaelk's suggestion is good...'tho you say you've already seen the line in root's crontab, yes?