Arduino Serial working only at first upload with USB

Development Tools IDE 1.x
1

Hi there,
i am working with Arduino USB connected: one week ago, if I plugged out the USB and re-plugged in Arduino, serial communication was perfect (TX led showing, USB serial monitor worked etc...)
Everything was perfect, then I choose to buy a more solid box and to rewire all the cables.
Now, I don't know why, Arduino sends serial data (TX led blinking) only when code is uploaded the first time. If i plug the USB cable out and re-plug in the cable, TX led doesn't blink and serial monitor doesn't show anything.

Can you help me? I have an imminent project to send and I am panicking

thanks

2

Another thing: Arduino should transmit serial data. i am testing it now... sometimes arduino doesnt get recognized by the PC. yesterday it was working perfectly.
when my pc recognizes it, TX doesn't blink anyway... until i don't open serial monitor. then it blinks and data gets transmitted.
is normal that tx blinks only when connected to usb? even if tx is not blinking, should arduino send serial data anyway? why doesn't arduino send serial data when usb connected?