Not much of a boffin, but I'll have a go
1)Assuming you're using Win9x and IE, go to the control panel, and double click on "Internet Options" (Or Tools>Internet Options if the browser is open.)
2)Click on the "Programs" tab at the top, and check that your default email program name shows in the "E-mail" drop box.
3)If nothing is there, click on the expansion arrow on the right of that box, and click the name of the email prog you use.
4)If no joy, open the email prog itself and find its options settings, and look for something like "make this your default email program" or words to that effect.
Hopefully this will sort the problem. You might also consider reinstalling the program in case setting it as default was an option overlooked during the original installation.
Just some ideas...good luck.
RGDS/Sq