It happens when there some change in your system setting, some time some virus or worm make some change in your Registry.
By the help of your operating system registry editor you can easily get back your default extension..
for this solution you have to follow these step:-
for those step click here.....
By the help of your operating system registry editor you can easily get back your default extension..
for this solution you have to follow these step:-
for those step click here.....