Cannot upload sketches to Arduino Uno R3 — avrdude: stk500_recv(): programmer is not responding

Update:
I have been told (in the first answer to this question) that I should install the Windows drivers for the ATmega 16U2 chip onboard my Arduino. Unfortunately, I have been unable to locate these drivers (I am looking specifically for Windows 10 drivers). Any help with that would be much appreciated. Thanks!

I recently got an Arduino Uno R3 board from Inland Electronics with an ATmega328. I know that it has a bootloader because it has Blink pre-uploaded; whenever I plug it in to my computer, the pin 13 LED flashes every other second. Since I have had it, I have not been able to upload any sketches to the board.

I am using the Arduino IDE 1.6.7 on a computer running Windows 10 Pro 64-bit. I have researched my problem and have been unable to find a fix, albeit trying everything that I can find. I have been trying to upload a slight modification to Blink, to make the LED blink faster. Nothing is connected to the board other than the USB cable to the computer. The code compiles just fine, as well.

I will begin by sharing the main error message I have received, then give some additional information. My error message:

Arduino: 1.6.7 (Windows 10), Board: "Arduino/Genuino Uno"

Sketch uses 1,030 bytes (3%) of program storage space. Maximum is 32,256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2,039 bytes for local variables. Maximum is 2,048 bytes.
C:\Program Files (x86)\Arduino\hardware\tools\avr/bin/avrdude -CC:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -carduino -PCOM3 -b115200 -D -Uflash:w:C:\Users\(my username)\AppData\Local\Temp\build9c9ef3bdfe2fccb480bc6e4bac749e41.tmp/Blink.ino.hex:i

avrdude: Version 6.0.1, compiled on Apr 15 2015 at 19:59:58
         Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
         Copyright (c) 2007-2009 Joerg Wunsch

         System wide configuration file is "C:\Program Files (x86)\Arduino\hardware\tools\avr/etc/avrdude.conf"

         Using Port                    : COM3
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0xcf
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0xcf

avrdude done.  Thank you.

Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

  This report would have more information with
  "Show verbose output during compilation"
  enabled in File > Preferences.

I have tried pressing the reset button at various different times in the process, for varying lengths of time, to no effect whatsoever. Some more information follows:

• All USB connections are secure
• The RX LED flashes briefly after each "attempt"
• All drivers are up to date and installed
• In Device Manager, my Arduino is shown as "Arduino Uno (COM3)". No other COM ports are shown as being used
• I have selected "Arduino/Genuino Uno" under "Board" in the IDE
• I have selected "COM3 (Arduino/Genuino UNO)" under "Port" in the IDE
• The programmer that was selected on installation of the IDE (and that still is selected) is "AVRISP mkll"

• I have changed the COM port to COM4 resulting in: avrdude: ser_open(): can't open device "\\.\COM4": The system cannot find the file specified.

• I changed it back to COM3 resulting in: avrdude: ser_open(): can't open device "\\.\COM3": Access is denied.

• I then completely uninstalled the Arduino software (after disconnecting the board)

• I followed the steps to reinstall on the "Getting Started With Arduino" page on arduino.cc
• I then began getting the original error again

I shared this information based on what other sites and questions have mentioned as being fixes (none of them worked for me).