Arduino uno not in sync

Arduino: 1.6.4 (Mac OS X), Board: "Arduino Uno"

Sketch uses 2,488 bytes (7%) of program storage space. Maximum is 32,256 bytes. Global variables use 194 bytes (9%) of dynamic memory, leaving 1,854 bytes for local variables. Maximum is 2,048 bytes. avrdude: stk500_recv(): programmer is not responding avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00 avrdude: stk500_recv(): programmer is not responding

This report would have more information with "Show verbose output during compilation" enabled in File > Preferences. i am making simple knock sensor, this is the first time this has happened to me ( i have used the peizo sensor 3 times for different projects) and i would love a suggestion or two :) I'm still very new to this so any advice is helpful

What is connected to the Arduino? Where? Something is interfering with the communication between the PC and the Arduino.

nothing is attached to the arduino other than the pc , and nothing is attached or running on the pc either. i also have up to date drivers.