Do you have the 4GB patch installed? You need it if you have a 64-bit OS and more than 2GB RAM. SH3 is an old program and doesn't know to address the extra RAM until you implement this patch:
http://www.subsim.com/radioroom/down...o=file&id=2888
or
http://www.gamefront.com/files/16964....exe-file.rar/
h.sie's patcher will add the 4 GB patch, too.
http://www.mediafire.com/download/27...1-Patch-Kit.7z
Try any one. I think it may fix your problem.
Good luck and good hunting! See you at the cabaret!