What are the historical dates of Daniel's 70th week showing that the birth and death of the Messiah has already taken place precisely as prophesied by Daniel?

The 70 weeks correspond with the year 445 B.C., or the twentieth year of Artaxerxes (Nehemiah 2:1-8). Each week represents seven years. I can't explain it any better than Dr. J. Vernon McGee did in his book, Thru The Bible, Volume 3, page 588:

Sixty-two weeks, or 434 years, bring us to the Messiah. Sir Robert Anderson in his book, The Coming Prince, has worked out the time schedule. From the first of the month Nisan to the tenth of Nisan (April 6) A.D. 32, are 173,880 days. Dividing them according to the Jewish year of 360 days, he arrives at 483 years (69 sevens). On this day Jesus rode into Jerusalem, offering Himself for the first time, publicly and officially, as the Messiah.

After the 69 weeks, or 483 years, there is a time break. Between the sixty-ninth and seventieth week two events of utmost importance are to take place:

1. Messiah will be cut off. This was the crucifixion of Christ, the great mystery and truth of the Gospel.

2. Destruction of Jerusalem, which took place in A.D. 70, when Titus the Roman was the instrument.

Daniel wrote, “And after threescore and two weeks shall Messiah be cut off but not for himself.” The Hebrew Bible makes this point even clearer: “And after those 62 weeks, the anointed one will disappear and vanish.” We entered the endtimes at that point. However, the 70th week has not yet been fulfilled: “And he shall confirm the covenant with many for one week.” That's the work of the Antichrist, who will complete the 70th week of years with the Great Tribulation.