|Most commonly this is fixed by correcting the default settings|
Open Internet Explorer.
On the Tools menu, click Internet Options.
Click the Advanced tab, and then click the Reset button.
On the Programs tab, under Internet programs, click Set Programs, then "Set your Default Programs", select your e-mail program and click "Set this program as Default". Repeat for Internet Explorer.
Click OK and close the dialogs.
Have you uninstalled any programs in the last couple of days?