Nokia 5800 Xpress Music — data lost from memory card

Address:

Barwani, Madhya Pradesh

i have been baught a nokia 5800 xpress music phone and using it from last 2 years, few days ago when i am downloading an application nokia e mail from nokia ovi store, after installation it ask for restart mobile to complete the installation, after restarting the mobile all the data has been lost and memory card is empty.
The memory card is not showing the data but it is showing that storage of data that it has stored earlier.
Please help me to recover my data or how i can get it back