User form - disable checkboxes until ready

I have closed my previous thread and raised this one, as I felt I may not have explained myself very well last time.
I have a User form that people must select their name from the drop down list and then select a number of check boxes.
I wanted the Check boxes to remain disabled until a person actually selected their name from the combo box.
The person's preferences are sent to another sheet but some people are sending preferences without their name.
I was given a suggestion of 'CB01.Enabled = False', but could not get it to work.
The combo Box opens with a blank field initially, so that's when I would like the Check Boxes to be greyed out.
As soon as the person selects their name, the check boxes become enabled.
Could somebody tell me if there is some VBA code I can attach somewhere which will do what I want?
Thank you to anybody that can assist me.