You might try, in order:

=> Starting IE7 in No Add-ons mode:

Right-click on the blue IE desktop icon and select Start without Add-ons;
or...

Start > (All) Programs > Accessories > System Tools > Internet Explorer (No
add-ons).

Troubleshooting and Internet Explorer’s (No Add-ons) Mode:
http://blogs.msdn.com/ie/archive/2006/07/25/678113.aspx

=> Resetting IE7 Settings (RIES)
http://support.microsoft.com/kb/923737 <= Read before using!

=> Check for and install any firmware upgrades for the router (and possibly
then reinstalling the router).

=> Check your MTU settings.  See http://support.microsoft.com/?kbid=315008 
(ignore the subject), paying particular attention to the third NOTE section.
Two very useful tools for this are the Tweak Test (followed by) Dr TCP, both
found here: http://www.dslreports.com/tools

And finally:

=> If you uninstall (a) IE7 (which automatically returns you to IE6), (b)
all toolbars and (c) all third-party Windows Themes (including Window
Blinds) and do NOT reinstall IE7, does this behavior persist?

Uninstalling IE7
http://www.ie-vista.com/kbase2.html

How to uninstall Internet Explorer 7:
http://support.microsoft.com/kb/927177

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

Also useful:

How to troubleshoot network connectivity problems in Internet Explorer:
[ignore the APPLIES TO section]
http://support.microsoft.com/kb/936211

Good luck.