Uno won't upload

Hello, im new to arduino, sadly i'm already running into technical difficulties.. :|

I'm running windows XP and after successfully uploading the "Example 01 : Blinking LED" sketch to my Arduino UNO, a few days later I decided to move on to "Example 02: Turn on LED while the button is pressed". But to my dissapointment the Arduino simply didn't respond in any way, just continues to blink using the original sketch.

error message reads:

Binary sketch size: 1018 bytes (of a 32256 byte maximum) avrdude: stk500_getsync(): not in sync: resp=0x00 avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51

So far i've tried;

disconnecting the breadboard

pushing the reset button on the arduino

pushing the reset button on the arduino at just before the sketch is uploaded.

The only lights that are lit are the ON light and the blinking L light. + I assume the sketch must be correct as I copied and pasted it from; http://makezine.com/getstartedarduino/

Any help will be greatly appreciated.

p.s also tried other usb ports.

protocol error, expect=0x14, resp=0x51

This means that the software sent out a signal and it heard back something, but it wasn't want it expected (the arduino sends back 0x14, and the other thing sent back 0x51).

You mentioned USB ports; was that plugging the arduino into a different physical port? What you should do is try all of the COM ports enumerated in the tools -> serial ports menu.

If none of those work, you'll have to go into the device manager and see if your computer recognizes the arduino at all. (I assume you already installed the drivers needed.)