Arduino UNO R3 cannot be detected by Windows XP

Hello All,

I am new to Arduino. Recently I have bought an Arduino R3 and install all the drivers and IDE as usual. It works fine for a few days and suddently it cannot be detected in Windows XP. It shown "Unknown Device" under the USB interface. I cannot reinstall the drivers, it always said "unknown device" is the best driver u can install.

I try to upload the bootloader via another arduino uno R3. The upload is success, but when I connect the board to the PC again, it cannot be detected either. I try the DFU mode to update the firmware, but I cannot enter the DFU mode even I have short the two pins required.

If I cannot detect the arduino board by PC, what can I do to fix it? Thanks for all your kind advice.

more info: When i am connecting the arduino, the LED on pin13 will blink in 3 times an interval.

Manual (official) option:

Automatic option:,118440.0.html