programmer is not responding

Hello everyone. I just recently got an Arduino Uno for my school projects. But whenever I want to upload a program/sketch on it, it shows me the classic error: "not in sync: resp=0x9f"

I checked out the different options and I checked everythihg
+The drivers ARE installed on the board
+I've selected the correct board model and the right COM port
+The board isn't over a conductive surface

The weirdest thing is that the "Blink" program comes out every time I connect the board in my computer, and I tryed to delete it uploading a blank program or modifying the delay values on the program, but this doesn't work either. Can you please tell me a good and 100% effective solution?
Even I tryed to change the COM port of the board on the device manager, but it doesn't work either.

Thanks in advance

I'm running an Arduino UNO board on Windows 7 32bit

You said you selected the correct COM port. If you remove arduino from pc, does the port disappear?

Yes, it does dissapear

Maybe you selected the wrong board type. Can you post a pic of your board?