First, you must uninstall NI-Daq software, either the version 5 and version 5.x software.
When you try to reinstall version 5.f, pay careful attention to the way it loads.
There are two things at work here. The NI-DAQ software loads itself, but it also loads the DAQ VI's into your version of LabVIEW so that LabVIEW can access the NI-DAQ drivers. If this part of the installation isn't ocurring, you'll see exactly what is happening with your system.
Mark