Before installing IE 7 you need to carefully follow the pre-installation
preparation described here:
http://www.ie-vista.com/known_issues.html#pre-install.

If you did not, you may have an incomplete or damaged installation of IE
7. In that case you should 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 directly from Microsoft and install from your hard disk:
http://www.microsoft.com/windows/downloads/ie/getitnow.mspx

Other troubleshooting steps:

1- Start IE 7 with no add-ons.

Start Internet Explorer from a shortcut on your desktop with the
following target (don't forget the quote marks):

"C:\Program Files\Internet Explorer\iexplore.exe"  -extoff

If the problem no longer occurs, one (or more) add-ons was causing the
problem.

2- Reset IE 7 to its original configuration.

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

If the problem no longer occurs, one (or more) incorrect configuration
settings was causing the problem. [If you want to continue to use any of
your add-ons after a reset, you may have to reinstall them.]

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

---
Leonard Grey
Errare humanum est

Assuming you updated IE7 after installing it:

Error message after you install a Windows Internet Explorer 7 update from
Windows Update or from Microsoft Update: "Webpage cannot be displayed":
http://support.microsoft.com/kb/942818

If tweaking your third-party firewall's settings don't help, try the
following:

1. Disable your anti-virus application, all Norton Add-ons (if any), any
real-time protection provided by an anti-spyware application (except for
Windows Defender; includes Spybot Tea Timer, SpySweeper Guards, AVG AS
guard.exe, etc.), disable any third-party firewall AND THEN enable the
Windows Firewall.

NB: You're "working without a net" now: Don't to ANYTHING else online (e.g.,
browsing; reading email; chatting) except #4 below until your anti-virus
application has been re-enabled!  If you're running ZA Free firewall, you
may need to uninstall it instead of disabling it.

2. Uninstall "Security Update for Windows Internet Explorer 7 (KB950579)"
via Add/Remove Programs (make sure Show Updates box is checked at top right)
and reboot.

3. Re-do #1 above.

4. Go to http://windowsupdate.microsoft.com and install any Critical Updates
offered.  If  a Root Certificates update is listed in the Optional Updates
category, install it to take full advantage of IE7's enhanced security.

5. Reboot > Make sure everything in #1 above is enabled again and, if
applicable, disable the Windows Firewall and enable (or reinstall) your
third-party firewall.

=====================================

For home users, no-charge support is available by calling 1-866-PCSAFETY in
the United States and in Canada or by contacting your local Microsoft
subsidiary.  There is no-charge for support calls that are associated with
security updates.  When you call, clearly state that your problem is related
to a Security Update and cite the update's KB number (e.g., KB123456).

LOOK! => If your problem relates to a Cumulative Security Update for IE,
call the above number and ask to be transferred to the Consumer IE7 queue
(which is 47830).

For more information about how to contact your local Microsoft subsidiary
for security update support issues, visit the International Support Web
site: http://support.microsoft.com/common/international.aspx

For enterprise customers, support for security updates is available through
your usual support contacts.

Start a free Windows Update support incident request:
https://support.microsoft.com/oas/default.aspx?gprid=6527

Support for Windows Update:
http://support.microsoft.com/gp/wusupport