My CD key or unique identification doesn't work

Updated: 06/30/2020 by Computer Hope

This page is for users having trouble entering their CD key, product key, or unique identification and not for users who have lost their unique identification number. If you have lost your license information, see: How to get a new unique identification number if lost.

The unique identification number or CD key that comes included with the software or your computer should always work. However, there are different reasons that cause the number not to work, as mentioned below.

Entering the wrong code

If you are installing Windows and the code you are entering is not working, make sure it is the correct code. With many OEMs, (e.g., Dell, Hewlett Packard, etc.) the manufacturer will place the code used with your computer on the back or bottom of it. Use this code to install Windows on your computer. However, realize that if your computer shipped with Windows XP and you're trying to install Windows Vista, the code on your computer only works for Windows XP. You would need to use the Windows Vista code that came with the software package.

Microsoft Windows XP Product Key

Below are some additional reasons a Microsoft Windows product key may not work.

  • Each version of Windows has its own unique product key, meaning a Windows XP Home product key won't work for Windows XP Professional.
  • A Windows upgrade product key won't work for a full version of Windows.
  • A Microsoft Windows OEM (original equipment manufacturer) product key won't work with retail versions of Windows.

Using the wrong character

Make sure all the letters and numbers you are entering are correct. Characters, such as the capital letter "O" and the number "0," can be difficult to read. Make sure you're entering an "O" and not a zero if that is what needs to be entered. Other problem letters include a capital letter "i" that looks like a lowercase "l," or a lowercase letter "l" that looks like the number "1."

If you tried all combination of letters and numbers, enter the key code as someone else reads it out loud.

Maximum installed copies

As a form of protection many programs, especially games, only allow a few copies of the program to be installed. If you have shared the unique identification number with friends or installed the program onto multiple computers, you may have reached the maximum allowed copies that can be installed.


Never share your unique number or software with your friends or family.

Product key disabled

The program is a pirated copy and using an invalid or disabled product key. Downloading a program from the Internet or buying a program from an auction site, such as eBay, are two common ways a scammer may distribute pirated software. If you tried the above suggestions and cannot get the program to accept the key code, the product key is likely disabled or was never legitimate.

Request new product key

Finally, you can contact the developer of the program to see if a new product key or CD key can be given over the phone. However, if they decide you've purchased a pirated copy or have exceeded the maximum allowed installations, they will not give you a new number.