The Alert Editor window can be brought up from various places - usually through the right click menu for specific symbols, for example on a Portfolio or a Raw Data window. You can also bring it up directly from the Dashboard or, in case of the Trendline Alerts, from the Annotation Parameter Editor.

 

 

The Alert System, as a whole, can be enabled/disabled on the Dashboard Status Bar, if disabled it will show with a red line through it on the status bar ()