iexplore.exe does not respond

Hi:

I just got a new desktop and ie7 was installed when running windows
update. It didn't work well and I decided to uninstall it. ie6 was
back. However, ie6 now slows the pc significantly. When I close ie6, I
can still see iexplore.exe running in the task manager. Plus, when I
want to turn off the computer, it says that iexplore.exe doesn't
respond and I have to press "End now" 2 to 3 times to be able to turn
off the computer.

The behavior that I just described does not happen every time I run
ie6 (i.e.: iexplore.exe is not running in the task manager after I close ie6). I will say the problem happens 50% of the time.

Any clues to what is going on Or how can I fix it

Thanks for your help!
Herman