last week i downloaded the Darkness 2 (great game) on XBL and when i was downloading it i lost conection to XBL 2 times but every time i connect again the download would resume where it left off, but know when i am downloading Kingdom of amalur Reckoning demo i lost connection 1 time and when i connect again it did not resume where it left of, does anyone know why

You probably have a poor Internet connection.

Well, there's your problem. You're using an Xbox.

 

With a bad connection.

Try resetting the router and if that doesn't work, the modem.

 

If that doesn't work. Hit it with a hammer. Hammers fix everything.

Like the others have said, you might just have a poor connection. Just go into your Xbox's storage and delete the incomplete demo, then try downloading it again. Demos are free, after all.