Error message when you start Internet Explorer 7 or try to access a Web
site: "Internet Explorer cannot display the Webpage"
http://support.microsoft.com/kb/926431

If that isn't it, I know of three other causes for the vast majority of such
problems:
1. You might have incompatible add-ons:
Go to Start | All Programs | Accessories | System Tools
and click Internet Explorer (No Add-ons).

2. Tools | Internet Options | Advanced
Scroll to the bottom and click Reset Internet Explorer Settings.  Read this
article first:
How to use Reset Internet Explorer Settings (RIES):
http://support.microsoft.com/kb/923737
Note that the Reset IE Settings button will delete AutoComplete data (such
as passwords.) Do you have those backed up?

3. Malware already installed on the computer:  Help with malware
All  MS-MVP Sites.
http://aumha.org/a/parasite.htm
http://aumha.org/a/quickfix.htm
http://www.elephantboycomputers.com/page2.html#Removing_Malware
http://mvps.org/winhelp2002/unwanted.htm
http://inetexplorer.mvps.org/darnit.html
http://www.mvps.org/sramesh2k/Malware_Defence.htm

Unexplained computer behavior may be caused by deceptive software.
http://support.microsoft.com/kb/827315

So How Did I Get Infected Anyway?
For quite a few people it's by installing programs like Messenger Plus,
whose ads for
malware don't identify the malware as such and try to convince you that you
owe it to the author.  See also:
http://www.wilderssecurity.com/showthread.php?t=27971
Don't ever do a "default" install of anything.  Always choose Custom and see
what else is being carried along.  Don't install any extras you're not sure
of.

You might also try the steps here:
"Internet Explorer stops responding, stops working, or restarts"
http://support.microsoft.com/gp/pc_ie_intro