From what I gather, you clicked the orange Launch Registration button on the Confirm page of Event Setup, however people are still unable to register.
There is most likely a very easy solution for this - and it most likely has to do with the registration launch dates/times you entered on the Classes + Categories page. For instance, let's say you set your participant classes to open at 8am on March 17. If you click the Launch Registration button on February 1st, participants will be able to access the first page of registration, but they won't be able to begin the registration process until 8am on March 17. Let's check it out:
If all dates look correct, check the start times...
Registration should be open!!
Here's a helpful hint for you:
Monday @ 12pm = noon on Monday
Monday @ 12am = 1 minute before 12:01 am on Monday (as opposed to 1 minute before 12:01 on Tuesday)