No one thing made Rome fall. When any government exists for as long as Rome did, things sort of pile up, many of which have already been mentioned.
A few things to remember however:
1)the Roman empire did NOT fall all at once, and it did not end in 476, the usual date given.
The Eastern Empire, which was certainly a continuation of the Imperial government, existed until the Muslims conquered it in the Middle Ages.
2)Even the barbarians who wound up bringing about the fragmentation and eventual disintegration of the Western Empire still saw the existence of the Roman Empire as a GOOD thing. Indeed, well into the era of the Rennaisance there was a government in Germany known as the Holy Roman Empire, in a futile attempt to keep something of Rome alive.
3)If anything can be said to have been the last straw that brought Rome down, it was a fragmentation of governmental power. Several different pretenders declared themselves Emporer on a semi-regular basis over a couple centuries and took troops from the borders into France and Rome to press their claim. This weakened the borders, weakened the military and threw doubt on the imperial authority. This, more than anything else, sapped Rome of both its troops and its wealth.