I can't upload a simple sketch to my arduino

Hi everybody:
I am not new in this kind of problems, but I tried everything for 1 hour and I am beginning to go crazy...
So I would appreciate any kind of help or advice.
Well first a little bit of history... I have my Arduino genuino, I bought it 4 years ago, from while to while I face problems uploading, this is because of I have a Macbook Pro. Well, my macbook has Yosemite, and until yesterday I had no problem uploading; but today, today is a different story I was trying to upload a simple blinking program and I got the next errors:

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

My first steps were:
-Yes, the ON LED is on.
-Yes, I am choosing Arduino/Genuino Board.
-Yes, I am connected to "dev.cu.usbmodem1411" (I am going to explain more of this later, don't worry...)
-Yes, I have nothing connected to my Arduino.
-Change the USB cable. (Silly, but helps sometimes)

I know what you are thinking about in my serial I should have "dev.tty.usbmodem1411", I don't have it like an option in my port selection. However, since I am Mac OS X user I know how to check my serial ports, so I went directly to my terminal and I written:
ls dev/tty.*
And my answer was:
/dev/tty.Bluetooth-Incoming-Port /dev/tty.usbmodem1411
/dev/tty.Bluetooth-Modem

And yup "/dev/tty.usbmodem1411" is the serial port that I was looking for and never appear on my Arduino IDE.

Then I accepted my problems on Mac, and only because of my urgency I borrowed a Windows 8.1 with the latest Arduino IDE. So I though that my problem was "solved", I connected the Arduino, and the PC recognized the Arduino easy, but again the same problem:

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0xd0

I don't know what else can I do...
I'd appreciate all your help
Martin