Modules and Themes invisible under Build Menu

Kindly help me out please. I am unable to see the modules and themes section under Build. Only I can approach module is by choosing "By module" in administrator page. If I try to access modules and themes page through unclean or clean url still i am unable to open the page. It returns back tto Build page. Also under create content page nothing is visible. This means I am unable to enable or disable modules or choose new themes or edit any theme. Please Please help me.
with regards
Amit