I don't claim to be an expert on DNA studies; I'm just learning. I have no personal experience with this, but have been considering its use. Maybe you'll decide that you've come to a dead end (no pun intended) and need to try something different. If so, this might be just the thing for you.
Here is a very simplified version of how it works. A long piece of DNA in males is passed down virtually unchanged from father to son. Surnames are generally passed down in the same fashion. So, a male should have the same Y chromosome as his father, grand-father, great-grandfather, and on and on... Amazing, isn't it! This means that two males with the same surname and same or similar Y chromosomes are often related through their paternal line.
That Y-DNA occasionally accumulates a harmless mutation before it is passed down to a son. These rare changes occur at a known rate, acting as a clock that can measure time. When testing reveals a relationship through the paternal line, this clock can be used to estimate the amount of time since their most recent common paternal ancestor. In this way, the men may be able to determine who that most recent common ancestor was and how their family branches diverged.
Surname studies can take advantage of this information and connect you with other members who might be closely or distantly related. These connections can also be important to adoptees. Because of nonexistent or missing paper records or confusing oral traditions, DNA testing can help fill in some gaps.
For more complete information on this, read Making Matches in the September 2010 family tree magazine. Also, check out the website for Sorenson Molecular Genealogy Foundation at: www.smgf.org