are you behind a proxy? (at work, school or on a public wifi?)
if so then we cannot help you bypass it.
if you are not behind a proxy (your own home network) then you ned to give us details such as:
-are you the owner of the network (if not, could someone have blocked access.. and if yes then talk to the owner)
-was it working before (ie maybe facebook had downtime or perhaps you blocked it accidentally somehow)
-anything else which you think is relevant.