i was running a labview software reading data from a DAQ card (NI USB-6008 and PCI-6225). the labview software was running fine but after sometimes (unknown period of time) the software sort of lost communication with the DAQ card. the software was still running but the analog input data from the DAQ card was not updated.
This may sound silly, but make sure you are connected properly. In one computer I was using the slightest movement of the instrument would shake loose the connection and it took me a little while to notice that it had happened.