I had the same thing happen to me last week. It seemed like it was one
of the NI services crashing. At one point I even restarted the machine
and fresh from booting, LabVIEW was sitting in the taskbar, stalled. I
tried to do a repair installation of LabVIEW 8 and that failed at step
19 when a service could not be stopped (sorry, I don't remember which
one). I think I was able to get the Repair operation to complete by
rebooting, stopping all the NI services manually, and then doing a
Repair. After that, everything seems fine.
I don't know what caused the problem in the first place, but I'm up and running again now.
Good luck,
Chris