Hi,
My client is having the same problem. His NX7.5 cannot be open but NX8.5 and NX9 can. I believe this is not software related issue, nor a license related issue. One thing we have tried out is we remove the user profile, and add in a new user profile, and things seems to work as normal. But after sometime, the NX7.5 again cannot be opened.
The syslog file indicates something like
*** COLLAPSE:: in line 2727 of D:\workdir\reference\NX755_4\src\syss\error\ind\error.cxx at Tue Jul 08 09:40:07 2014 Malay Peninsula Standard Time
+++ Unhandled operating system exception: c0000005
I believe this is related to permission of the user. If you tried to start NX7.5 with administrative right, probably NX7.5 can open without problem. Currently we are asking GTAC about it as well.
Kind regards,
Tuw