Pin 13 LED always blink

hello , ihave arduino uno rev 3 it was working fine until i start to test all the examples in the arduino sofware after that the Led on PIN 13 dosen't stop blinking and no other program work on my arduino i try evry things i googled but no answer please help me .

It might be broken, and you have to buy a new one.

If you have a programmer, you could try the ICSP header (6 pins (2x3) on the board), but that won't help a lot, because I think it is broken.