Arduino Mega2560 USB connection not working

I was working on my robot the other day and after 2 hours of uploading and testing new code, the comm port suddenly died out. I unplugged and plugged the cable back in. I reinstalled the drivers. I tried to plug the arduino into other computers. I tried with different cables. It still won't work. A USB cable will power the device, but nothing else.

The arduino itself is still operable. It sends out PWM signals and follows the flawed logic I uploaded the last time, but it won't be recognized as a device on any computer. This leads me to believe the USB connection is the problem. Either the hardware itself or the driver on the device. I have asked many people, but they have not been able to help me fix this problem.

Is there anything I can do to fix this? I know the processor and the peripherals still work, but the communication with a computer is not working.

There are many similar threads, try to find inspiration in these (for example):
http://forum.arduino.cc/index.php/topic,178994.0.html
http://forum.arduino.cc//index.php/topic,191873.0.html
http://forum.arduino.cc//index.php?topic=191983.0.html