Sometimes Google Analytics tracking code just stops working (i.e. does not fire anymore). Sometimes the tracking code fires but certain hits (like ‘event’ hit) just drop (i.e. not sent to the GA server).
In that case, your existing or new tracking code may not work. So how can you fix the problem?
Through the "Google Analytics Troubleshooting Guide" you can determine what has gone wrong and what can be done to fix the tracking issues.