Important license info:
If your period of free upgrade has expired (expires 12 months after purchase), you will not be able to get a new activation code if the license is not removed from your hard-drive using the "license removal" tool before changing the computer or changing/reformatting the hard-drive. Darts for Windows is licensed by computer, not user, that is the reason why the license has to be removed from the old computer/hard-drive before you can use it on a new computer or hard-drive.
The license removal tool removes the license from the computer and uploads a confirmation of the removal to the DfW license server.
After the removal, you will be eligible to register the new serial number you require a unlock code for on this page and also continue to get free updates, even if the period of free upgrade has expired.
If you fail to follow the license removal procedure or the license server is not able to register the license removal or you are not able to deactivate the old license due to various reasons, you will have to buy a new activation code to reactivate Darts for Windows.
A new activation code for Darts for Windows costs £10 if your period of free upgrades has expired. Click this link to buy a new activation code.

IF YOU ARE NOT ABLE TO REMOVE THE ORIGINAL LICENSE AND YOU NEED THE CODE FOR A NEW COMPUTER, YOU WILL HAVE TO PURCHASE A NEW LICENSE. REACTIVATION WILL ONLY WORK IF YOU ARE REACTIVATING THE SAME COMPUTER AS THE ORIGINAL LICENSE

Download the license removal tool from here.

On Windows Vista and Windows 7 the license removal tool must be run as administrator!

After the license has been removed, contact the author of Darts for Windows to make sure the license removal has been registered by the license server. When you have received the confirmation of the removal, you can now register the new license here.

This is how the license removal tool looks like: