child menu dissappear

the child menu in navigation that comes by default dissappear... i dnt know where i changed menu under site building, user management,content management disappears now there is only one sub menu blocks under site building others modules,views(i have install views modules and cck modules) theme configuration menu all disappear.. this is 2nd time happening to me plz i wud be so thankful if any one can help me..... reinstalling can solve it but i dont want to reinstall its not a solution i think .... what and where did i wrong to disappear plz help me out .....

thanks in advance