With the limited amount of info, it's tough to make a diagnosis.
Hardware:
Does your system meet the base requirements?
http://www.ni.com/labview/requirements#1
Additionally, I'm not sure w/ LV, but other applications require at least some swap memory space, wihch is a default option in XP. I'd make sure you haven't deactivated swap memory.
OS/non-LV software:
Does it give any error message?
Additoinally, you can check the event logs (Control Panel->Admin Tools->Event Viewer->Apps) to see where the fault is occuring.
Do other apps crash or is it only LV?
Are you logged in as an admin? Does the error always occur, or only as a limited user?
Are any other apps/background programs (virus, non-windows utilities) running? Does the error occur w/
all of these closed down?
LV Specific:
Are you running LV locally or remotely?
Do you now or previously have had other versions of LV installed? Some people, although I haven't personally seen it, have had issues w/ missing drivers and other weirdness when other versions are present or even have been removed.
Are you trying to run a vi, or does it crash when opening LV itself (eg at the splash screen)?
Last resort:
There's always the option of doing a clean XP install, followed immediately after by a clean LV install.
2006 Ultimate LabVIEW G-eek.