Problem to use this program!

It is not unusal for software to be issued which allows you to use it for a limited period before requiring you to verify that it is a legal copy by giving the serial number. So if you acquired it legitimately, there should be a serial number somewhere in the box in which the program was marketed.
If for some reason you have lost or thrown out the required piece of paper, then you should contact the manufacturer or distributor of the product and explain your problem. This information is usually on the disc itself, and if necessary you can do a search on the web to locate the manufacturer/distributer, and then email your problem. What happens from there I don't know. They may require you to post back the disc, so that they can replace it with another one which has a serial number. I hope you can make some sense out of all this.