saravananm92:
from the symptoms you mentioned,your guess seems to be correct.Did you try with a different cable?
yeap, 2-3 different ones. I really hope that i'm wrong, otherwise its usefulness becomes really limited. 
SurferTim:
How were you powering the Mega when the fail occurred? Were you powering it with the 5v bus? Powering the Mega with the 5v bus and the USB at the same time can cause that fail.
well, i'm not sure when the damage (?) occurred exactly, but usually i was powering it through a 9v battery. When i realized the fault, i think i was just connected to it through usb.