Hi,
Guessing that you've installed IE7, check for an incompatible browser
add-on.
See: http://www.enhanceie.com/ie/troubleshoot.asp
for troubleshooting information.
More at:
IEBlog  Troubleshooting and Internet Explorer’s (No Add-ons) Mode:
http://blogs.msdn.com/ie/archive/2006/07/25/678113.aspx

The troublesome program may not show up as an add-on. Disable other
security, privacy, ad-blocking, appearance tweaking programs to see if one
of them is causing the problem. Any program that interacts with Internet
Explorer could be causing this.

A firewall will probably not be causing this problem, but be sure to turn on
the Windows Firewall from Control Panel> Windows Firewall before disabling a
third-party firewall or security suite during testing.

More troubleshooting procedures:
936214- How to troubleshoot compatibility problems that affect IE7 in
Windows Vista
(also applicable to XP)
http://support.microsoft.com/kb/936214

Hope this helps,
Don
[MS MVP- IE]