What type of card are you using? If it is a non-NI card, then it will not show up in MAX. You will still be able to run programs using the card, you just won't be able to use MAX.
If it is an NI card, then run the NI-488.2 Getting Started Wizard and Select Board Type and Configure. Ensure that the configuration is correct and use the "OK" button to save the configuration (if you use the "X" in the top corner, it's the same as cancel). Then try MAX again.
Hope this helps.
Rob