Naveen..

This is a very open questin.... to prevent this happening again.. you need to have understanding of your app and then you need to understand why it happened...

Below are some good links which you can refer to start your investigation...

http://msdn.microsoft.com/en-us/library/ms178104.aspx

http://www.sqlservercentral.com/Forums/Topic514877-146-1.aspx#bm515674

and here you need to provide as much as info you've to get to the point answer... as there can be 100s of reason for this to happen.... so post all the info you've or can gather... and lets see what we can make out of that....:-)

Tell me if this helps....

Rohit