The good news is this is usually fixable. There's a comprehensive list of steps below, and hopefully going through it will help get everything running smoothly. Here's what to do:

Windows 95/98/Me

Edit the File Association:

1. Double-click My Computer on the desktop.
2. On the View menu, click Folder Options (or Options).
3. Click the File Types tab.
4. Click URL: HyperText Transfer Protocol in the Registered File Types box.
5. Click Edit.
6. In the Actions box, click Open.
7. Click Edit.
8. Click Browse.
9. Navigate to the \Program Files\Internet Explorer folder.
10. Click the Iexplore.exe file.
11. Click Open.
12. Click OK.
13. Click Close.
14. Click Close again.

Please note that you may also need to repeat these steps for the following file associations:

URL:HyperText Transfer Protocol with Privacy
URL:File Transfer Protocol
URL:Gopher Protocol

Here's how to set Internet Explorer to check whether it's the default browser:

1. Click Start and select Settings.
2. Click Control Panel.
3. Double-click Internet.
4. Click the Programs tab.
5. Click to select Internet Explorer. Look to see if there's a check in the box indicating it's the default browser.
6. Click Apply.
7. Click OK.
8. Start Internet Explorer.
9. Click OK when you're prompted to make Internet Explorer the default browser.

For Windows NT/2000/XP

Edit the File Association:

1. Double-click My Computer on the desktop.
2. On the Tools menu, click Folder Options (or Options).
3. Click the File Types tab.
4. Click URL:HyperText Transfer Protocol in the Registered File Types box.
5. Click Advanced.
6. In the Actions box, click Open.
7. Click Edit.
8. Click Browse.
9. Navigate to the \Program Files\Internet Explorer folder.
10. Click the Iexplore.exe file.
11. Click Open.
12. Click OK.
13. Click OK again.
14. Click Close.

Please note that you may also need to repeat these steps for the following file associations:

URL:HyperText Transfer Protocol with Privacy
URL:File Transfer Protocol
URL:Gopher Protocol

Now here's how to set Internet Explorer to check whether it is the default browser:

1. Click Start and select Settings.
2. Click Control Panel.
3. Double-click Internet Options.
4. Click the Programs tab.
5. Click to select the Internet Explorer. Look to see if there's a check in the box indicating it's the default browser.
6. Click OK.
7. Start Internet Explorer.
8. Click OK when you're prompted to make Internet Explorer the default browser.