Go to \ColdFusion10\cfusion\lib and locate license.properties. Open this file in notepad or wordpad and then you will find the ColdFusion 10 Serial number there. If not, then please type in your license key, save the file and Restart the ColdFusion services.
This should work for you.
Thanks. It worked this way ...however, the serial number was already there ... restarting using windows' service manager did the trick.don't know why.