user8405: NOTE: Using the Arduino Uno
I am WORKING on a project that I have to submit in a few days. My arduino was all set up and was working fine. 
Project:Arduino controls a 9v motor depending on the command given. As the arduino only provides 5v , i added a 9v battery to it through a transistor
I decided to add new code into the arduino but when I tried it failed. I have uploaded code thousands of times before (successfully) all of a sudden the IDE keeps giving the following message

avrdude: ser_open(): can't open device "\.\COM3": Access is denied.

I have looked up for a lot of solutions on this forum and elsewhere. Here are the things I have tried so far:

Changing the COM port 
Disabling all the other devices CONNECTED to COM
Tightening the CONNECTIONS
Re installing all the drivers and the IDE
Rebooting the system
Using another laptop to upload code

All the above have given me the same output for some reason. The built in LED light and the power LED switch on when the board is CONNECTED to a power source (my laptop). Could the board have been damaged by any chance ? How can I check if the board is spoilt ? Should I buy a new board ? 

user8420: Have you tried changing the Microprocessor in the Arduino Uno?
An AtMega320P is much cheaper than new Arduino, and usually only the microprocessor gets spoilt, rest of the board remains intact.

user14716: Could be the OS not allowing the application to access the COM ports, there is a terminal command to give the Arduino IDE access to the specific COM port.

user10794: I have a post Have I bricked my Arduino Uno? Problems with uploading to board - that describes various tests you can carry out to isolate where the problem is.

8405: <p>NOTE: Using the Arduino Uno</p>

<p>I am WORKING on a project that I have to submit in a few days. My arduino was all set up and was working fine. </p>

<p>Project:Arduino controls a 9v motor depending on the command given. As the arduino only provides 5v , i added a 9v battery to it through a transistor</p>

<p>I decided to add new code into the arduino but when I tried it failed. I have uploaded code thousands of times before (successfully) all of a sudden the IDE keeps giving the following message</p>

<blockquote>
  <p>avrdude: ser_open(): can't open device "\.\COM3": Access is denied.</p>
</blockquote>

<p>I have looked up for a lot of solutions on this forum and elsewhere. Here are the things I have tried so far:</p>

<ol>
<li>Changing the COM port </li>
<li>Disabling all the other devices CONNECTED to COM</li>
<li>Tightening the CONNECTIONS</li>
<li>Re installing all the drivers and the IDE</li>
<li>Rebooting the system</li>
<li>Using another laptop to upload code</li>
</ol>

<p>All the above have given me the same output for some reason. The built in LED light and the power LED switch on when the board is CONNECTED to a power source (my laptop). Could the board have been damaged by any chance ? How can I check if the board is spoilt ? Should I buy a new board ? </p>
 8420: <p>Have you tried changing the Microprocessor in the Arduino Uno?
An AtMega320P is much cheaper than new Arduino, and usually only the microprocessor gets spoilt, rest of the board remains intact.</p>
 14716: <p>Could be the OS not allowing the application to access the COM ports, there is a terminal command to give the Arduino IDE access to the specific COM port.</p>
 10794: <p>I have a post <a href="https://arduino.stackexchange.com/questions/13292/have-i-bricked-my-arduino-uno-problems-with-uploading-to-board">Have I bricked my Arduino Uno? Problems with uploading to board</a> - that describes various tests you can carry out to isolate where the problem is.</p>
