Communication problem on Arduino Mega 2560

Hi guys! I was using my arduino mega as usual some months ago with no problem. Today i got it again to work on new things and my notebook was not able to recognize it anymore via usb cable! the programm that i wrote before is working properly but my windows is not recognizing it.

I have tried to communicate with another usb cable and with another notebooks and still had the same communication problem. I also tried to press the reset button on the board, but nothing happens! The old programm still there working and i the communication problem was not solved. does someone know who to fix it?

Thanks!

Do you have the driver installed for it?

Does the program that you last loaded still run when you provide external power such as from a power brick or 9V battery?