If you have tumbled across a problem where your drop down menus are going behind your text, images or flash etc then the following information would help you sort that out. The menus going behind text and images is usually an Internet Explorer problem but the menus going behind flash files chode be Internet Explorer, Chrome or Firefox.
All you need to do is to give a higher z-index to the menu div and that should put it on top of the stack and hence will not hide under any text or images.
i.e. z-index: 9999;
For this you will have to do some extra work;
If the problem still persists, please feel free to leave your comments below and i will try to provide any possible assistance.