If your campaign has stopped sending this indicates a problem. Check the bounce and complaint rates for the campaign, if either of these are too high then the campaign may have been automatically blocked. A bounce rate over 10% or a complaint rate over 1% is considered too high!
For assistance resolving high bounce rates please see the following topic:
My campaign has a high number of bounces
Once you have resolved the issue you can request to have the campaign un-blocked so that it will continue sending. To request an unblock please open a support ticket by emailing [email protected].