hadoop startup problem

[asmaa.atef]

hello everyone,
i have a problem in hadoop startup ,every time i try to start hadoop name node doesnot start and when i tried to stop name node ,it gives an error :no name node to start.
i tried to format the name node and it works well ,but now i have data in hadoop and formatting name node will erase all data.
what can i do?
thanks in advance,
asmaa