Help! Arduino Mega 2560 connection problem

Hi, I faced trouble while using Arduino Mega 2560 and had no idea what is going on.

It had been working quite well but suddenly my computer cannot notice arduino!
My arduino IDE doesn't recognize any COM port.

and Says: Window is unable to install your arduino mega 2560 dfu
window could not find driver software for your device

Ive already tried with device manger of window but it didn't work.

Please help!