I have installed WIndows 7(64 bit) Ultimate, before by pressing FN key, there was small display which used to come on my Display, showing,which bottons works for what but now there isn't any thing showed when I press that FN key.FN + F8, FN+f9,FN+F10,FN+11,FN+12, doesn't work any more.
What you mean are Toshiba Flash Cards. If you press an FN key, on display the Flash Cards appear and show you what happens if you press F1 for example.
This is a Toshiba feature so you must install Toshiba Value Added Package and Flash Cards Support Utility. Your notebook is listed on the Toshiba US page so you can download everything here: http://www.csd.toshiba.com/