It sounds like the default browser has been changed, have you installed google chrome or firefox recently? Have you uninstalled google chrome or firefox? If you use Internet Explorer we can quickly reset that to the default browser following these instructions:
1. Open Internet Explorer
2. Click the settings button at the top right and click Internet Options. You can also do this by clicking Tools>Internet Options from the menu bar.
3. Click on the "Programs" tab (2nd tab from the right).
4. There should be a button that says "Make Default" Click this button. There is a check box under the make default but slightly to the left that says "Tell me if Internet Explorer is not the default web browser." put a check in that box.
5. Close internet Explorer and re-open it. Try to click on your links again from email.