sketches will not upload to board

several years ago I got an uno, which worked fine with our windows computer. now, using it on a macbook air, I had it occasionally get stuck uploading without stop. I tried to install drivers because I thought this might help. I don't remember if it worked once afterwards and then stopped or not, but now it will never upload. As far as I can tell, the I've completely removed the drivers, but it still will not upload sketches. Here is the error.

Arduino: 1.8.5 (Mac OS X), Board: "Arduino/Genuino Uno"

Archiving built core (caching) in: /var/folders/22/b38pk7bj78z1tmybq65dg4x80000gn/T/arduino_cache_350576/core/core_arduino_avr_uno_1910dc4c15bc5d5c82673360f14ded58.a Sketch uses 928 bytes (2%) of program storage space. Maximum is 32256 bytes. Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes. /Users/ziadk/Desktop/Arduino.app/Contents/Java/hardware/tools/avr/bin/avrdude -C/Users/ziadk/Desktop/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf -v -patmega328p -carduino -P/dev/cu.usbmodem1411 -b115200 -D -Uflash:w:/var/folders/22/b38pk7bj78z1tmybq65dg4x80000gn/T/arduino_build_805633/Blink.ino.hex:i

avrdude: Version 6.3, compiled on Jan 17 2017 at 12:01:35 Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/ Copyright (c) 2007-2014 Joerg Wunsch

System wide configuration file is "/Users/ziadk/Desktop/Arduino.app/Contents/Java/hardware/tools/avr/etc/avrdude.conf" User configuration file is "/Users/ziadk/.avrduderc" User configuration file does not exist or is not a regular file, skipping

Using Port : /dev/cu.usbmodem1411 Using Programmer : arduino Overriding Baud Rate : 115200 avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x00 avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x00

avrdude done. Thank you.

An error occurred while uploading the sketch

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