This is a problem I ran into recently. I have a 64-bit operating system.

I’m running Excel 2010, which is 32-bit. There is also a 64-bit version. (You can get this information by going to File > Help.)

I went to Programs > Administrative Tools > Data Sources (ODBC). I set up a System DSN. I tested it and it works fine. Hurray!

Then I opened Excel 2010 and went to Data > From Other Sources > From Microsoft Query. The DSN isn’t there. What happened?

I scratched my head over this for a while, and then emailed my team. One of my senior DBAs had run into this before and pointed me to this Microsoft KB article: On a 64-bit computer, the DSN will be set up as 64-bit. However, a 32-bit application can’t see a 64-bit DSN. Excel 2010 is a 32-bit application.
To solve this problem, I needed to set up a 32-bit DSN. I did that by going running the 32-bit ODBC Data Source Administrator tool from C:WindowsSysWOW64odbcad32.exe. I created the same DSN, with _32Bit in the name.

I went back to Excel > Data > From Other Sources > From Microsoft Query. My 32-bit DSN is in the list.

What I learned is that 64-bit operating systems contain both 64-bit and 32-bit ODBC administration tools. You must use the appropriate tool for the application you are working with.