I have original Arduino Uno made in Italy. After use for nearly two years without problem, I can't load program to arduino and L ie pin 13 is always HIGH from last week. I had tried lot to figure out problem but unfortunately it didn't work!!! Once removing atmel ,still LED is high! Is there any solution over it??? Changing USB port will b a solution??
Thanks in advance!! 
Does the loopback test work?http://forum.arduino.cc/index.php?topic=73748.0
It sounds like the bootloader and/or the internal fuses are mangled. It can be repaired, but perhaps you can just replace the chip in the board. Shops such as Sparkfun sell the, 28 pin ATMega 328p chip that is the heart of your Uno. The new chip costs less than $4 iirc. With the board unplugged, just pry the old chip out, and press in the new one (making sure you have it the right way 'round.)
Be sure to get a new chip with the bootloader already programmed onto it. They will say if it does.