Read this post below and see if anything in there helps. One other thing, check the switch mounted to the turret shaft to see that it is not partially depressed.
Also, there (I think) is a sensor somewere on top of the draw bar that tells the machine that the tools is released. This could be one problem. (Someone correct me if I'm wrong on this one).
Anyway do searches for "Fadal ATC"...
http://www.cnczone.com/forums/fadal/...ure_alarm.html (ATC TURRET FAILURE and ALARM)