It is certainly safer to start a new career whenever you introduce any major new mod.
The exact answer to your question rather depends on what mods you had previously.
I would advise going to your folder 'my documents', locate sub-folder SH3 and rename it to something else (for example 'XXXSH3XXX'). Then start a new career.
If NYGM now works, we have answered your question.
If NYGM does not work, then there is some kind of file error, and you may need to reinstall.
If you are using SH3Commander, be sure to roll it back before you make any of the above changes.
If all else fails, you can always revert to your original mod(s), delete the new folder My Documents\SH3, and rename your folder XXXSH3XXX to SH3.
Stiebler.
NYGM Tonnage War Mod - Leading Edge Realism