THe best thing to do is to check to see what IRQ is currently assigned to your DAQCard, and determine if any other devices in your system are also using that same IRQ. If there is a conflict, then the problems you described will occur. Ways to resolve it include disabling or changing the IRQ of the other conflicting device to another IRQ value, or changing the IRQ your DAQCard is using to a value which is currently unused.
The following thread discusses a similar issue and gives suggestions:
http://forums.ni.com/ni/board/message?board.id=250&message.id=5394
I am curious, which IRQ values have you attempted to use thus far with no luck ?