If you have Vista, IE 7 cannot be uninstalled or reinstalled.

If you have XP, you likely have an incomplete or damaged installation if
you did not carefully follow the pre-installation preparation described
here:

http://www.ie-vista.com/known_issues.html#pre-install.

Uninstall IE 7 (which returns you to IE 6) by following these directions:

http://support.microsoft.com/kb/927177
...and...
http://www.ie-vista.com/kbase2.html

and then re-install IE 7 following the directions above. Download the IE
7 installer from Microsoft and install directly from your hard disk:
http://www.microsoft.com/windows/downloads/ie/getitnow.mspx

This frequently works better than going through Microsoft/Windows Update.

How do you know your problem is caused by Internet Explorer? Experience
has shown that virtually all problems reported here concerning Internet
Explorer 7 are not caused by the browser.

1- Start IE 7 with no add-ons. If the problem no longer occurs, one (or
more) add-ons was causing the problem.

For Windows XP: All Programs > Accessories > System Tools > Internet
Explorer (No Add-ons)

For Windows Vista: Type Internet Explorer in the Start Search box >
click Internet Explorer (No Add-Ons)

2- Reset IE 7 to its original configuration. If the problem no longer
occurs, one (or more) incorrect configuration settings was causing the
problem.

Tools > Internet Options > Advanced tab > under Reset Internet Explorer
Settings, click Reset.

Note: If you want to continue to use any of your add-ons after a reset,
you'll have to reinstall them.

3- Most third party security applications interact with Internet
Explorer to protect your computer from malicious software. Check the
settings in your security software to see if this is happening to you.

4- Problems with IE 7 can also be caused by the presence of viruses or
other malicious software.

---
Leonard Grey
Errare humanum est