my mega will not start working until I open the serial monitor

Hi guy, Im trying too get two megas two talk serially, my programs load ok. But the program will not begin until I open the serial monitor
I know because as soon as It opens the TX led starts flashing, if I close the serial program it keep going. But if I remove the power and reconnect
it, the mega just sits doing nothing until I open the serial monitor. How do I get it to run for the off