Hello Colin,
The best way to test NI cards is using a utility called Measurement and Automation Explorer (MAX). This should be an icon on your desktop or available from the start menu. From here, you can test all aspects of your devices.
If you open up MAX and expand the +My System section of the tree and the +Devices and Interfaces and the +NI-DAQmx Devices sections of the tree. You should see listed the NI 6025e cards. If you right-click on the card and select 'Test Panels' a test dialog will pop-up. Connect some known DC signals to the channels on the card that are giving off readings. Then on the analog input tab, select each of these channels in turn and then run the test panel and observe the values being read.
If you observe a stable reading here from all the channels then it may be a problem with the software you are using to acquire data. If a stable reading isn't possible, please post details of the signals you have connected, and also the version of the NI-DAQ driver you have and the operating system you are using. From this information I'll be able to look into these problems further.
Regards
Hannah
NIUK and Ireland