If alerts aren't working, there are a number of things you can do to troubleshoot. Here are some suggestions - and feel free to check out our support pages for more information.
Make sure you're "Watching" a host with the alert.
By far, the most common reason that an alert isn't working is because it isn't tied to an IP address. An alert won't just start working automatically - you need to tell it which host(s) you want that alert to watch.
To attach an alert to an IP, trace to the host you're interested in. Then, right-click on the hop you want to monitor and select "Watch this host (Alerts)..." from the menu.
Note that if you're tracing to a destination that doesn't respond, and you want to watch that destination (even though it's not on the upper graph), just right-click on the time-graph on the bottom and this same menu item should be on that menu.
From here, you can move an alert from the "Available" to the "Selected" list. Any alerts on the "Selected" list will watch this host whenever this host is involved in any route (be it an intermediate host, or the final destination).
When a host is being watched by the alert system, there will be brackets around the hop number in the upper graph. If those brackets aren't showing, then that host isn't being watched. This should put a [...] around the hop that's being monitored.
Set up an alert that will fire instantly, with an event that is very evident.
If you have an alert set up - and tied to a host (see above), but it seems like the alert isn't working, then changing your alert parameters (or create a new "test" alert).
Set up "Traces to Examine:" to 10. Alert when "1" or more traces are over 1ms.
Unless your network is responding in 1ms or less, this alert will fire on the first collected sample with the alert enabled.
For an event type, use "Play a sound", or "Tray icon change/notification" as both of these events happen immediately with no wait. In addition, for the "Play a sound", use "each time alert conditions are met (repeating)", as this will continuously make sound, rather than just when conditions start / stop.
Using this sequence, you should be able to tie an alert to just about any host and have the alert conditions fire immediately. Now, add on another event type (ie: email).
You can leave multiple events tied to a single alert - that way you can continue to hear the sound while you're troubleshooting another event type.