Arduino Not Uploading

Hello,

I am having this weird issue that won't allow me to upload code to my Arduino Uno. Last time I used it, it worked fine. Now I am using the same laptop, same USB port, same USB cord, and same Uno. When I try uploading, sometimes it gives me this message:

avrdude: ser_open(): can't open device "\\.\COM16": Access is denied.

and sometimes it tells me "uploading..." but never actually uploads.

Upon further review, it only happens with this one Uno, but I am not sure why. I don't know if it is the COM port, or if the Arduino is fried (unlikely). I checked my device manager and made sure I have my settings the same as every other port. I made sure I had the proper port selected in tools>port before uploading. I tried several times, so it isn't a one-time thing. Anyone know why this might be?

A couple of things come to mind.

  1. Possible bootloader issue. Usually fixed by uploading the bootloader
  2. Laptop so possible power issues on the laptop. Usually fixed by inserting a decent quality POWERED USB 2.0 hub between the lappy and the Arduino.
  3. USB connection issues caused by loose USB sockets. Sometimes fixed by checking and re-soldering.

this is the new error message it gave me:

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0xca
avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0xca
Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

What does a search for "stk500" give you if you use the search box at the top of the page ?
You could narrow that search using "resp=0xca"