If you have installed DataConnect on a 64 bit machine then you will need to have 64 bit drivers for your database installed. If you do not have suitable drivers installed you will see an error which states "Data source name not found and no default driver specified" when you test your connection in DataConnect.
Seeing What Drivers are Installed
You can use the Drivers tab of the ODBC Data Source Administrator (Administrative Tools -> Data Sources (ODBC)) to see which drivers are installed:
On a 64 bit machine this dialog will show you which 64 bit drivers you have installed. If you wish to see which 32 bit drivers are installed on a 64 bit machine, you will need to double-click on odbcad32.exe in C:\Windows\SysWOW64 to run the 32 bit version of the ODBC Data Source Administrator:
If the driver for your database only appears in the 32 bit list then you will either have to install a 64 bit driver or switch to running the 32 bit version of DataConnect. See here for instructions on how to switch DataConnect versions.