why does it say error 21 or error 3014 when i try to install my iphone 4

Hi

when ever i try to restore my iphone 4 it always says "error 21" or it would say "error 3014" error 21 is the most common and im not sure what to, do ive tried everything that it says to do and no difference i have the lastest version of itunes and the latest version of windows 7 and still nothing. the only reason i have to install it is because i left it on my draw and when i went back to it it was on the floor. and by the way the back glass isnt on and wasnt on at the time. i picked it up and i attempted to turn it on and the apple sign kept going and cmoing back so i instantly knew it needed restoring as i have done it before but this didnt happen. but then when i took the case off thatbwas protecting the battery and all the other stuff inside the iphone the bateery just fell out and this never happened before. so i freaked out and thoought my phone was broken but then i connected it to itunes and it turned on so i was releived. but then thats when the errors statred happening..

can someone help me please