Hello storm, I cannot give you a definite answer, but often some virus' will stop any av software or firewalls from starting. May I suggest that you ensure that your av protection is up-to date, then run a full scan. If that shows clean, try reinstalling ZA to see if that cures the problem.
Also, do you have any other firewalls installed? Or have you installed or changed any other software recently (ie just before this problem occurred)? And should you need to post back, please let us know which OS you are using and what version of ZA you have installed!!
Regards, Mr. Mouse.