It's been recommended to use .cmd files since Windows NT - only use a .bat file if you actually *need* the 16bit command.com interpreter. I cannot think of many scenarios nowadays where a script would need access to the 16bit interpreter (what you have posted here certainly does not), as the 32bit cmd.exe does pretty much everything you should need - since 1993!

Most likely your menu.bat has an exit command or something similar in it, which would cause startnet.cmd to finish. You need startnet to start something else that will "hold" it open, such as a start /w cmd.exe.