Incompatible add-ons is usually the cause.
What if you right click the IE icon on the desktop and choose Start Without Add-ons?
Or go to Start/ All Programs/ Accessories/ System Tools/ Internet Explorer (No Add-ons).
The Google ToolBar is suspect as well.
You may want to read this; Unexplained Computer Behavior May Be Caused by Deceptive Software
And if nothing else works,scan your computer for malware/spyware.
What programs do you presently have installed?