How many times have you restarted NX since it initially crashed? What caused the crash (ie, what were you doing when it crashed)? Have you looked at your temp file directory and emptied it since the crash? There are a plethora of things that could be causing this slowness - it could just be the restart and once you get to using it again, things go back to normal.
Tim Flater
NX Designer
NX 9.0.2.5 Win7 Enterprise x64 SP1
Intel Core i7 2.5GHz 16GB RAM
4GB NVIDIA Quadro K3100M