If uninstalling IE7 and returning to IE6 resolved the problem, you may have
had a "horked" install of IE7, for any number of reasons.

Required reading IMHO before installing IE7:

Sandi's Installation Tips <= Steps #1-8, #10 & #11; take note of #12, then
STOP!
http://www.ie-vista.com/known_issues.html#pre-install
(ignore any references to Vista)

And I strongly recommend using
http://www.microsoft.com/windows/downloads/ie/getitnow.mspx as the
installation source, not Automatic/Windows Update.

Alternately, use this Direct Download link:
http://www.microsoft.com/downloads/details.aspx?familyid=9ae91ebe-3385-447c-8a30
-081805b2f90b

Tip: Save the installer to your desktop, do not Run it.

Make *certain* that you check in at Windows Update immediately after
installing IE7 and install any critical updates offered.  If Optional
Updates category offers Root Certificates update, I recommend installing it
to take full advantage of IE7's additional security.

IEBlog : IE7 Installation and Anti-Malware Applications
http://blogs.msdn.com/ie/archive/2006/10/11/IE7-Installation-and-Anti_2D00_Malwa
re-Applications.aspx

What's New in Internet Explorer 7
http://msdn.microsoft.com/en-us/library/ms649487.aspx

Release Notes
http://msdn2.microsoft.com/en-us/ie/Aa740486.aspx

IEBlog: IE and Windows XP Service Pack 3
http://blogs.msdn.com/ie/archive/2008/05/05/ie-and-xpsp3.aspx

I know of three 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