1. Check that you have used .show() method on the toast object as an initial troubleshooting step.
2. Also check if there are any error logs in LogCat.
3. Make sure that you are working on the UI thread.
4. Try changing the contexts and try : MyActivity.this or this or getApplicationContext()
If everything looks fine, yet no Toast displayed then check the Android OS version your running the App.
Since Jelly Beans 4.2 (API level 16) users can disable App level Notifications by going to : Settings -> Applications -> Manage Applications -> AnyApp -> uncheck "Show Notification"
Note : When the Notification is disabled, Apps will not display any notification on Notification bar also it will not display any Toast messages for that app.
So an user running Jelly Beans or Higher may disable Notifications for you app, this as an adverse effect of this, no toast message will be displayed for you app too!