i have a problem in system preferences in desktop & screen saver it is not working ?

when i open the desktop & screen saver, system prefernces is not work not responding .

it is stop working and not work

i can not change my background picture

please help me

MacBook Air

Processor 1.86 GHz Intel Core 2 Duo

Memory 2 GB 1067 MHz DDR3

Graphics NVIDIA GeForce 320M 256 MB

Software OS X 10.8.3 (12D78)